学術論文 on 池田思朗

Ring Asymmetry and Spin in M87$^\ast$

Sun, 01 Mar 2026 00:00:00 +0000

The Astrophysical Journal, vol. 1000, no. 2, pp. 231(21pp)

著者:

Vadim Bernshteyn
Nicholas S. Conroy
Michi Baub"ock
Paul Tiede
Abhishek V. Joshi
Ben S. Prather
Charles F. Gammie
The Event Horizon Telescope Collaboration

URL:

DOI
arXiv

Abstract:

Event Horizon Telescope (EHT) images of the supermassive black hole M87* depict an asymmetric ring of emission. General relativistic magnetohydrodynamic (GRMHD) models of M87* and its accretion disk predict that the amplitude and location of the ring’s peak brightness asymmetry should fluctuate due to turbulence in the source plasma. We compare the observed distribution of brightness asymmetry amplitudes to the simulated distribution in GRMHD models, across varying black hole spin $a_\ast$. We show that, for strongly magnetized (MAD) models, three epochs of EHT data marginally disfavor $\|a_\ast\|łesssim 0.2$. This is consistent with the Blandford-Znajek model for M87’s jet, which predicts that M87* should have nonzero spin. We show quantitatively how future observations could improve spin constraints and discuss how improved spin constraints could distinguish between differing jet-launching mechanisms and black hole growth scenarios.

Majorization-minimization Bregman proximal gradient algorithms for NMF with the Kullback–Leibler divergence

Thu, 01 Jan 2026 00:00:00 +0000

Journal of Optimization Theory and Applications, vol. 208, pp. 14(34pp)

著者:

Shota Takahashi
Mirai Tanaka
Shiro Ikeda

URL:

DOI
arXiv

Abstract:

Nonnegative matrix factorization (NMF) is a popular method in machine learning and signal processing to decompose a given nonnegative matrix into two nonnegative matrices. In this paper, we propose new algorithms, called majorization-minimization Bregman proximal gradient algorithm (MMBPG) and MMBPG with extrapolation (MMBPGe) to solve NMF. These iterative algorithms minimize the objective function and its potential function monotonically. Assuming the Kurdyka–Łojasiewicz property, we establish that a sequence generated by MMBPG(e) globally converges to a stationary point. We apply MMBPG and MMBPGe to the Kullback–Leibler (KL) divergence-based NMF. While most existing KL-based NMF methods update two blocks or each variable alternately, our algorithms update all variables simultaneously. MMBPG and MMBPGe for KL-based NMF are equipped with a separable Bregman distance that satisfies the smooth adaptable property and that makes its subproblem solvable in closed form. Using this fact, we guarantee that a sequence generated by MMBPG(e) globally converges to a Karush–Kuhn–Tucker (KKT) point of KL-based NMF. In numerical experiments, we compare proposed algorithms with existing algorithms on synthetic data and real-world data.

Probing jet base emission of M87$^\ast$ with the 2021 Event Horizon Telescope observations

Thu, 01 Jan 2026 00:00:00 +0000

Astronomy & Astrophysics, vol. 706, pp. A27(20pp)

著者:

Saurabh
Hendrik Müller
Sebastiano D. von Fellenberg
Paul Tiede
Michael Janssen
Lindy Blackburn
Avery E. Broderick
Erandi Chavez
Boris Georgiev
Thomas P. Krichbaum
Kotaro Moriyama
Dhanya G. Nair
Iniyan Natarajan
Jongho Park
Andrew Thomas West
Maciek Wielgus
The EHT Horizon Telescope Collaboration

キーワード:

accretion
accretion disks / black hole physics / gravitation / relativistic processes / galaxies: individual: \messierbib / galaxies: jets

URL:

DOI
arXiv

Abstract:

We investigate the presence and spatial characteristics of the jet base emission in M87* at 230 GHz, enabled by the significantly enhanced $(u,v)$ coverage in the 2021 Event Horizon Telescope (EHT) observations. The integration of the 12 m Kitt Peak Telescope (USA) and NOEMA (France) stations into the array introduces two critical intermediate-length baselines to SMT (USA) and IRAM 30 m (Spain), providing sensitivity to emission structures at spatial scales of $\simeq250 µas$ and $\simeq2500 µas$ ($\simeq0.02 pc$ and $\simeq0.2 pc)$. Without these new baselines, previous EHT observations of the source in 2017 and 2018 lacked the capability to constrain emission on large scales, where a ``missing flux’’ of order $\simeq1 Jy$ is expected to reside. To probe these scales, we analyzed closure phases-robust against station-based gain calibration errors-and model the jet base emission using a simple Gaussian component offset from the compact ring emission at spatial separations $>$100 µas. Our analysis revealed a Gaussian feature centered at ($\Delta {\mathrmRA}\approx 320 µas$, $\Delta {\mathrmDec.}\approx60 µas$), projected separation of $\approx5500 AU$, with an estimated flux density of only $\sim60 mJy$, implying that most of the missing flux identified in previous EHT studies had to originate from different, larger scales. Brighter emission at the relevant spatial scales is firmly ruled out, and the data do not favor more complex models. This component aligns with the inferred position of the large-scale jet and is therefore physically consistent with the emission of the jet base. While our findings point to detectable jet base emission at 230 GHz, the limited coverage provided by only two intermediate baselines limits our ability to robustly reconstruct its morphology. Consequently, we treated the recovered Gaussian as an upper limit on the jet base flux density. Future EHT observations with expanded intermediate baseline coverage will be essential to constrain the structure and nature of this component with higher precision.

Spatially resolved polarization swings in the supermassive binary black hole candidate OJ 287 with first Event Horizon Telescope observations

Thu, 01 Jan 2026 00:00:00 +0000

Astronomy & Astrophysics, vol. 705, pp. A23(24pp)

著者:

Jos'e L.} {G'omez
Ilje Cho
Efthalia Traianou
Thomas P. Krichbaum
Guang-Yao Zhao
Rocco Lico
Antonio Fuentes
Marianna Foschi
Rohan Dahale
Boris Georgiev
Kotaro Moriyama
Maciek Wielgus
Roman Gold
Dominic W. Pesce
Hendrik} {M"uller
Svetlana Jorstad
Teresa Toscano
Jan} {R"oder
Jos'e M.} {Mart'\i
Manel Perucho
Yuri Y. Kovalev
Stefanie Komossa
Achamveedu Gopakumar
Mauri J. Valtonen
Gabriele Bruni
Sunil Chandra
The Event Horizon Telescope Collaboration

キーワード:

black hole physics / instabilities / radiation mechanisms: non-thermal / techniques: interferometric / galaxies: active / galaxies: individual: OJ 287

URL:

Abstract:

We present the first Event Horizon Telescope 1.3 mm observations of the supermassive binary black hole candidate OJ~287. The observations achieved an unprecedented angular resolution of 18 µas and reveal significant structural and polarization variability over just five days, marking the shortest timescale on which such changes have been directly imaged in this source. The inner jet exhibits a twisted ridgeline structure, with features displaying apparent superluminal motions up to about 22 c. The linear polarization maps reveal three main polarized features whose electric-vector position angles (EVPAs) change substantially over the time span of our observations, including a component with a radial polarization consistent with being produced by a recollimation shock. Most notably, we directly resolved two innermost jet components whose EVPAs rotate in opposite directions. The faster component, moving at $2.4\pm\qty[per-mode=symbol]0.9{µas\perday}$ ($17.4\pm6.5 c$), exhibits counterclockwise EVPA swings of roughly 3.7° per day, while the slower component, with a proper motion of $1.4\pm\qty[per-mode=symbol]0.3{µas\perday}$ ($10.2\pm2.2 c$), rotates clockwise at approximately 2.5° per day. Previous studies inferred helical magnetic fields in AGN jets from time-resolved or integrated polarization variability but lacked the angular resolution to directly image this effect. Our results provide spatially resolved evidence that a helical magnetic field threads the jet’s collimation and acceleration zone, ruling out models based on the superposition of unresolved components. Our analysis suggests that propagating shocks interact with a Kelvin-Helmholtz plasma instability, illuminating different phases of the helical magnetic field and producing the observed polarization spatial and temporal variability. Moreover, our model naturally accounts for the more rapid polarization rotation observed in the faster moving component. Our model predicts even more rapid swings in polarization, which could be tested with future observations featuring a more densely sampled time coverage.

Horizon-scale variability of M87$^\ast$ from 2017–2021 EHT observations

Mon, 01 Dec 2025 00:00:00 +0000

Astronomy & Astrophysics, vol. 704, pp. A91(37pp)

著者:

The Event Horizon Telescope Collaboration

キーワード:

accretion
accretion disks
black hole physics
gravitation
galaxies: active
galaxies: individual: M87
galaxies: jets

URL:

Abstract:

The Event Horizon Telescope (EHT) observation of M87* in 2018 has revealed a ring with a diameter that is consistent with the 2017 observation. The brightest part of the ring is shifted to the southwest from the southeast. In this paper, we provide theoretical interpretations for the multi-epoch EHT observations for M87* by comparing a new general relativistic magnetohydrodynamics model image library with the EHT observations for M87* in both 2017 and 2018. The model images include aligned and tilted accretion with parameterized thermal and nonthermal synchrotron emission properties. The 2018 observation again shows that the spin vector of the M87* supermassive black hole is pointed away from Earth. A shift of the brightest part of the ring during the multi-epoch observations can naturally be explained by the turbulent nature of black hole accretion, which is supported by the fact that the more turbulent retrograde models can explain the multi-epoch observations better than the prograde models. The EHT data are inconsistent with the tilted models in our model image library. Assuming that the black hole spin axis and its large-scale jet direction are roughly aligned, we expect the brightest part of the ring to be most commonly observed 90 deg clockwise from the forward jet. This prediction can be statistically tested through future observations.

Langevin Compton Imaging: A new method of visualizing radioactive sources based on Markov chain Monte Carlo

Sat, 01 Nov 2025 00:00:00 +0000

Nuclear Instruments and Methods in Physics Research A, vol. 1080, pp. 170815(9pp)

著者:

Yutaka Tsuzuki
Shiro Ikeda
Hiroki Yoneda
Tadayuki Takahashi

URL:

Abstract:

Compton imaging is an emerging method to visualize X- and gamma-ray sources. Regardless of the expanding use of the Compton imaging, most conventional image reconstruction methods do not derive uncertainties that should be defined on each resulting image. We propose a new Compton imaging method, named Langevin Compton Imaging, that defines uncertainties of Compton images in a statistically well-founded manner. We quantitatively evaluate the statistical significance of image features, such as the presence of multiple source peaks. Moreover, our method enables us estimate the intensity ratio between source peaks.

Maximum-expectation matching under recourse

Fri, 01 Aug 2025 00:00:00 +0000

European Journal of Operational Research, vol. 324, no. 3, pp. 732–741

著者:

Jo~ao Pedro Pedroso
Shiro Ikeda

URL:

DOI
arXiv

Abstract:

This paper addresses the problem of maximizing the expected size of a matching in the case of unreliable vertices and/or edges. The assumption is that the solution is built in several steps. In a given step, edges with successfully matched vertices are made permanent; but upon edge or vertex failures, the remaining vertices become eligible for reassignment. This process may be repeated a given number of times, and the objective is to end with the overall maximum number of matched vertices. An application of this problem is found in kidney exchange programs, going on in several countries, where a vertex is an incompatible patient-donor pair and an edge indicates cross-compatibility between two pairs; the objective is to match these pairs so as to maximize the number of served patients. A new scheme is proposed for matching rearrangement in case of failure, along with a prototype algorithm for computing the optimal expectation for the number of matched edges (or vertices), considering a possibly limited number of rearrangements. Computational experiments reveal the relevance and limitations of the algorithm, in general terms and for the kidney exchange application.

First polarization study of the M87 jet and active galactic nuclei at submillimeter wavelengths with ALMA

Tue, 01 Jul 2025 00:00:00 +0000

Astronomy & Astrophysics, vol. 699, pp. A265(17pp)

著者:

Ciriaco Goddi
Douglas F. Carlos
Geoffrey B. Crew
Lynn D. Matthews
Hugo Messias
Alejandro Mus
Iván Mart{'\i}-Vidal
Ezequiel Albentosa-Ru{'\i}z
Mariafelicia De Laurentis
Elisabetta Liuzzo
Nicola Marchili
Kazi L. J. Rygl
The Event Horizon Telescope Collaboration

キーワード:

black hole physics
magnetic fields
polarization
radiation mechanisms: non-thermal
instrumentation: interferometers
instrumentation: polarimeters
Astrophysics of Galaxies
High Energy Astrophysical Phenomena

URL:

DOI
arXiv

Abstract:

\em Aims. We investigated the polarization and Faraday properties of Messier 87 (M87) and seven other radio-loud active galactic nuclei (AGNs) at $łambda$ 0.87 mm (345 GHz) using the Atacama Large Millimeter/submillimeter Array (ALMA). Our goal was to characterize the linear polarization (LP) fractions, measure Faraday rotation measures (RMs), and examine the magnetic field structures in the emission regions of these AGNs. \em Methods. We conducted full-polarization observations as part of the ALMA Band 7 very long baseline interferometry (VLBI) commissioning during the April 2021 Event Horizon Telescope (EHT) campaign. We analyzed the LP fractions and RMs to assess the nature of Faraday screens and magnetic fields in the submillimeter emission regions. \\em Results. We find LP fractions between 1 % and 17 % and RMs exceeding d5 {rad m^-2}, which are 1–2 orders of magnitude higher than typically observed at longer wavelengths ($łambda>3 mm$). This suggests denser Faraday screens or stronger magnetic fields. Additionally, we present the first submillimeter polarized images of the M87 jet and the observed AGNs, revealing RM gradients and sign reversals in the M87 jet indicative of a kiloparsec-scale helical magnetic field structure. \em Conclusions. Our results provide essential constraints for calibrating, analyzing, and interpreting VLBI data from the EHT at 345 GHz, representing a critical step toward submillimeter VLBI imaging.

Origin of the Ring Ellipticity in the Black Hole Images of M87$^\ast$

Tue, 01 Jul 2025 00:00:00 +0000

Astronomy & Astrophysics, vol. 699, pp. A279(18pp)

著者:

Rohan Dahale
Ilje Cho
Kotaro Moriyama
Kaj Wiik
Paul Tiede
José L. Gómez
Chi-Kwan Chan
Roman Gold
Vadim Y. Bernshteyn
Marianna Foschi
Britton Jeter
Hung-Yi Pu
Boris Georgiev
Abhishek V. Joshi
Alejandro Cruz-Osorio
Iniyan Natarajan
Avery E. Broderick
León D. S. Salas
Koushik Chatterjee
The Event Horizon Telescope Collaboration

キーワード:

accretion
accretion disks
black hole physics
gravitation
galaxies: active

URL:

DOI
arXiv

Abstract:

We investigate the origin of the elliptical ring structure observed in the images of the supermassive black hole M87*, aiming to disentangle contributions from gravitational, astrophysical, and imaging effects. Leveraging the enhanced capabilities of the Event Horizon Telescope (EHT)’s 2018 array, including improved $(u,v)$-coverage from the Greenland Telescope, we measured the ring’s ellipticity using five independent imaging methods, obtaining a consistent average value of $\tau = 0.08_-0.02^+0.03$ with a position angle of $\xi = 50.1_-7.6^+6.2$ degrees. To interpret this measurement, we compared it to general relativistic magnetohydrodynamic (GRMHD) simulations spanning a wide range of physical parameters including the thermal or nonthermal electron distribution function, spins, and ion-to-electron temperature ratios in both low- and high-density regions. We find no statistically significant correlation between spin and ellipticity in GRMHD images. Instead, we identify a correlation between ellipticity and the fraction of non-ring emission, particularly in nonthermal models and models with higher jet emission. These results indicate that the ellipticity measured from the M87* emission structure is consistent with that expected from simulations of turbulent accretion flows around black holes, where it is dominated by astrophysical effects rather than gravitational ones. Future high-resolution imaging, including space very long baseline interferometry and long-term monitoring, will be essential to isolate gravitational signatures from astrophysical effects.

A multifrequency study of sub-parsec jets with the Event Horizon Telescope

Sat, 01 Mar 2025 00:00:00 +0000

Astronomy & Astrophysics, vol. 695, pp. A233(21pp)

著者:

Jan Röder
Maciek Wielgus
Andrei P. Lobanov
Thomas P. Krichbaum
Dhanya G. Nair
Sang-Sung Lee
Eduardo Ros
Vincent L. Fish
Lindy Blackburn
Chi-Kwan Chan
Sara Issaoun
Michael Janssen
Michael D. Johnson
Sheperd S. Doeleman
Geoffrey C. Bower
Geoffrey B. Crew
Remo P. J. Tilanus
Tuomas Savolainen
C. M. Violette Impellizzeri
Antxon Alberdi
Anne-Kathrin Baczko
José L. Gómez
Ru-Sen Lu
Georgios F. Paraschos
Efthalia Traianou
Ciriaco Goddi
Daewon Kim
Mikhail Lisakov
Yuri Y. Kovalev
Petr A. Voitsik
Kirill V. Sokolovsky
The Event Horizon Telescope Collaboration

キーワード:

accretion
accretion disks
black hole physics
gravitation
galaxies: active

URL:

DOI
arXiv

Abstract:

\em Context. The 2017 observing campaign of the Event Horizon Telescope (EHT) delivered the first very long baseline interferometry (VLBI) images at the observing frequency of 230 GHz, leading to a number of unique studies on black holes and relativistic jets from active galactic nuclei (AGN). In total, eighteen sources were observed, including the main science targets, Sgr A* and M87, and various calibrators. Sixteen sources were AGN. \em Aims. We investigated the morphology of the sixteen AGN in the EHT 2017 data set, focusing on the properties of the VLBI cores: size, flux density, and brightness temperature. We studied their dependence on the observing frequency in order to compare it with the Blandford-K"onigl (BK) jet model. In particular, we aimed to study the signatures of jet acceleration and magnetic energy conversion. \em Methods. We modeled the source structure of seven AGN in the EHT 2017 data set using linearly polarized circular Gaussian components (1749+096, 1055+018, BL Lac, J0132-1654, J0006-0623, CTA 102, and 3C 454.3) and collected results for the other nine AGN from dedicated EHT publications, complemented by lower frequency data in the 2–86 GHz range. Combining these data into a multifrequency EHT $+$ data set, we studied the dependences of the VLBI core component flux density, size, and brightness temperature on the frequency measured in the AGN host frame (and hence on the distance from the central black hole), characterizing them with power law fits. We compared the observations with the BK jet model and estimated the magnetic field strength dependence on the distance from the central black hole. Results. Our observations spanning event horizon to parsec scales indicate a deviation from the standard BK model, particularly in the decrease of the brightness temperature with the observing frequency. Only some of the discrepancies may be alleviated by tweaking the model parameters or the jet collimation profile. Either bulk acceleration of the jet material, energy transfer from the magnetic field to the particles, or both are required to explain the observations. For our sample, we estimate a general radial dependence of the Doppler factor $\delta\propto r^łe 0.5$. This interpretation is consistent with a magnetically accelerated sub-parsec jet. We also estimate a steep decrease of the magnetic field strength with radius $B\propto r^-3$, hinting at jet acceleration or efficient magnetic energy dissipation.

Smart Kanata: A Framework for Autonomous Decision Making in Rapid Follow-up Observations of Cataclysmic Variables

Sat, 01 Feb 2025 00:00:00 +0000

Publications of the Astronomical Society of Japan, vol. 77, no. 2, pp. 219–236

著者:

Makoto Uemura
Yuzuki Koga
Ryosuke Sazaki
Tomoya Yukino
Tatsuya Nakaoka
Ryo Imazawa
Taichi Kato
Daisaku Nogami
Keisuke Isogai
Naoto Kojiguchi
Kenta Taguchi
Yusuke Tampo
Hiroyuki Maehara
Shiro Ikeda

キーワード:

accretion disks
observational
dwarf novae
cataclysmic variables

URL:

DOI
arXiv

Abstract:

Studying the early stages of transient events provides crucial information about the fundamental physical processes in cataclysmic variables (CVs). However, determining an appropriate observation mode immediately after the discovery of a new transient presents challenges due to significant uncertainties regarding its nature. We developed a framework designed for autonomous decision making in prompt follow-up observations of CVs using the Kanata 1.5 m telescope. The system, named Smart Kanata, first estimates the class probabilities of variable star types using a generative model. It then selects the optimal observation mode from three possible options based on the mutual information calculated from the class probabilities. We have operated the system for $\sim 300$ days and obtained 21 samples, among which automated observations were successfully performed for a nova and a microlensing event. In the time-series spectra of the nova V4370 Oph, we detected a rapid deepening of the absorption component of the $H_\alpha$ line. These initial results demonstrate the capability of Smart Kanata in facilitating rapid observations and improving our understanding of outbursts and eruptions of CVs and other galactic transients.

Solving Self-calibration of ALMA Data with an Optimization Method

Sat, 01 Feb 2025 00:00:00 +0000

Publications of the Astronomical Society of Japan, vol. 77, no. 2, pp. 260–276

著者:

Shiro Ikeda
Takeshi Nakazato
Takashi Tsukagoshi
Tsutomu T. Takeuchi
Masayuki Yamaguchi

キーワード:

interferometric
image processing
data analysis

URL:

DOI
arXiv

Abstract:

We reformulate the gain correction problem of the radio interferometry as an optimization problem with regularization, which is solved efficiently with an iterative algorithm. Combining this new method with our previously proposed imaging method, PRIISM, the whole process of the self-calibration of radio interferometry is redefined as a single optimization problem with regularization. As a result, the gains are corrected, and an image is estimated. We tested the new approach with ALMA observation data and found it provides promising results.

The Persistent Shadow of the Supermassive Black Hole of M87, II. Model comparisons and theoretical interpretations

Wed, 01 Jan 2025 00:00:00 +0000

Astronomy & Astrophysics, vol. 681, pp. A265(27pp)

著者:

The Event Horizon Telescope Collaboration

キーワード:

accretion
accretion disks
black hole physics
gravitation
galaxies: active
galaxies: individual: M87
galaxies: jets

URL:

Abstract:

Broadband multi-wavelength properties of M87 during the 2018 EHT campaign including a very high energy flaring episode

Sun, 01 Dec 2024 00:00:00 +0000

Astronomy & Astrophysics, vol. 692, pp. A140(44pp)

著者:

J. C. Algaba
M. Balokovi'c
S. Chandra
W.-Y. Cheong
Y.-Z. Cui
F. D’Ammando
A. D. Falcone
N. M. Ford
M. Giroletti
C. Goddi
M. A. Gurwell
K. Hada
D. Haggard
S. Jorstad
A. Kaur
T. Kawashima
S. Kerby
J.-Y. Kim
M. Kino
E. V. Kravchenko
S.-S. Lee
R.-S. Lu
S. Markoff
J. Michail
J. Neilsen
M. A. Nowak
G. Principe
V. Ramakrishnan
B. Ripperda
M. Sasada
S. S. Savchenko
C. Sheridan
729 authors

キーワード:

galaxies: active
galaxies: individual: M87
galaxies: jets
galaxies: nuclei

URL:

DOI
arXiv

Abstract:

\em Context. The nearby elliptical galaxy M87 contains one of only two supermassive black holes whose emission surrounding the event horizon has been imaged by the Event Horizon Telescope (EHT). In 2018, more than two dozen multi-wavelength (MWL) facilities (from radio to $\gamma$-ray energies) took part in the second M87 EHT campaign.\em Aims. The goal of this extensive MWL campaign was to better understand the physics of the accreting black hole M87*, the relationship between the inflow and inner jets, and the high-energy particle acceleration. Understanding the complex astrophysics is also a necessary first step towards performing further tests of general relativity.\em Methods. The MWL campaign took place in April 2018, overlapping with the EHT M87* observations. We present a new, contemporaneous spectral energy distribution (SED) ranging from radio to very high-energy (VHE) $\gamma$-rays as well as details of the individual observations and light curves. We also conducted phenomenological modelling to investigate the basic source properties. \em Results. We present the first VHE $\gamma$-ray flare from M87 detected since 2010. The flux above 350 GeV more than doubled within a period of $\sim36$ hours. We find that the X-ray flux is enhanced by about a factor of two compared to 2017, while the radio and millimetre core fluxes are consistent between 2017 and 2018. We detect evidence for a monotonically increasing jet position angle that corresponds to variations in the bright spot of the EHT image.\em Conclusions. Our results show the value of continued MWL monitoring together with precision imaging for addressing the origins of high-energy particle acceleration. While we cannot currently pinpoint the precise location where such acceleration takes place, the new VHE $\gamma$-ray flare already presents a challenge to simple one-zone leptonic emission model approaches, and it emphasises the need for combined image and spectral modelling.

First Very Long Baseline Interferometry Detections at 870 ${\mu}$m

Thu, 01 Aug 2024 00:00:00 +0000

The Astronomical Journal, vol. 168, no. 3, pp. 130(19pp)

著者:

Alexander W. Raymond
Sheperd S. Doeleman
Keiichi Asada
Lindy Blackburn
Geoffrey C. Bower
Michael Bremer
Dominique Broguiere
Ming-Tang Chen
Geoffrey B. Crew
Sven Dornbusch
Vincent L. Fish
Roberto Garc{'\i}a
Olivier Gentaz
Ciriaco Goddi
Chih-Chiang Han
Michael H. Hecht
Yau-De Huang
Michael Janssen
Garrett K. Keating
Jun Yi Koay
Thomas P. Krichbaum
Wen-Ping Lo
Satoki Matsushita
Lynn D. Matthews
James M. Moran
Timothy J. Norton
Nimesh Patel
Dominic W. Pesce
Venkatessh Ramakrishnan
Helge Rottmann
Alan L. Roy
Salvador Sánchez
Remo P. J. Tilanus
Michael Titus
Pablo Torne
Jan Wagner
Jonathan Weintroub
Maciek Wielgus
André Young
The Event Horizon Telescope Collaboration

URL:

Abstract:

The first very long baseline interferometry (VLBI) detections at 870 µm wavelength (345 GHz frequency) are reported, achieving the highest diffraction-limited angular resolution yet obtained from the surface of the Earth and the highest-frequency example of the VLBI technique to date. These include strong detections for multiple sources observed on intercontinental baselines between telescopes in Chile, Hawaii, and Spain, obtained during observations in 2018 October. The longest-baseline detections approach 11 Głambda, corresponding to an angular resolution, or fringe spacing, of 19 µas. The Allan deviation of the visibility phase at 870 µm is comparable to that at 1.3 mm on the relevant integration timescales between 2 and 100 s. The detections confirm that the sensitivity and signal chain stability of stations in the Event Horizon Telescope (EHT) array are suitable for VLBI observations at 870 µm. Operation at this short wavelength, combined with anticipated enhancements of the EHT, will lead to a unique high angular resolution instrument for black hole studies, capable of resolving the event horizons of supermassive black holes in both space and time.

ALMA 2D Super-resolution Imaging of Taurus-Auriga Protoplanetary Disks: Probing Statistical Properties of Disk Substructures

Wed, 01 May 2024 00:00:00 +0000

Publications of the Astronomical Society of Japan, vol. 76, no. 3, pp. 437–474

著者:

Masayuki Yamaguchi
Takayuki Muto
Takashi Tsukagoshi
Hideko Nomura
Naomi Hirano
Takeshi Nakazato
Shiro Ikeda
Motohide Tamura
Ryohei Kawabe

キーワード:

ALMA
radio interferometer
protoplanetary disk

URL:

DOI
arXiv

Abstract:

In the past decade, ALMA observations of protoplanetary disks revealed various substructures including gaps and rings. Their origin may be probed through statistical studies on the physical properties of the substructures. We present the analyses of archival ALMA Band 6 continuum data of 43 disks (39 Class II and 4 Herbig Ae) in the Taurus-Auriga region. We employ a novel 2D super-resolution imaging technique based on sparse modeling to obtain images with high fidelity and spatial resolution. As a result, we have obtained images with spatial resolutions comparable to a few au ($0''.02 - 0''.1$), which is two to three times better than conventional CLEAN methods. All dust disks are spatially resolved, with the radii ranging from 8 to 238 au with a median radius of 45 au. Half of the disks harbor clear gap structures, whose radial locations show a bimodal distribution with peaks at $łesssim20 au$ and $\gtrsim30 au$. We also see structures indicating weak gaps at all the radii in the disk. We find that the widths of these gaps increase with their depths, which is consistent with the model of planet-disk interactions. The inferred planet mass-orbital radius distribution indicates that the planet distribution is analogous to our Solar System. However, planets with Neptune mass or lower may exist in all the radii.

Neural style transfer of weak lensing mass maps

Wed, 01 May 2024 00:00:00 +0000

The Open Journal of Astrophysics, vol. 7

著者:

Masato Shirasaki
Shiro Ikeda

キーワード:

weak lensing map
Cycle GAN

URL:

DOI
arXiv

Abstract:

We propose a new generative model of projected cosmic mass density maps inferred from weak gravitational lensing observations of distant galaxies (weak lensing mass maps). We construct the model based on a neural style transfer so that it can transform Gaussian weak lensing mass maps into deeply non-Gaussian counterparts as predicted in ray-tracing lensing simulations. We develop an unpaired image-to-image translation method with Cycle-Consistent Generative Adversarial Networks (Cycle GAN), which learn efficient mapping from an input domain to a target domain. Our model is designed to enjoy important advantages; it is trainable with no need for paired simulation data, flexible to make the input domain visually meaningful, and expandable to rapidly-produce a map with a larger sky coverage than training data without additional learning. Using 10,000 lensing simulations, we find that appropriate labeling of training data based on field variance allows the model to reproduce a correct scatter in summary statistics for weak lensing mass maps. Compared with a popular log-normal model, our model improves in predicting the statistical natures of three-point correlations and local properties of rare high-density regions. We also demonstrate that our model enables us to produce a continuous map with a sky coverage of $\sim166 \squaredeg$ but similar non-Gaussian features to training data covering $\sim12 \squaredeg$ in a GPU minute. Hence, our model can be beneficial to massive productions of synthetic weak lensing mass maps, which is of great importance in future precise real-world analyses.

First Sagittarius A$^\ast$ Event Horizon Telescope Results. VII. Polarization of the Ring

Fri, 01 Mar 2024 00:00:00 +0000

The Astrophysical Journal Letters, vol. 964, no. 2, pp. L25(32pp)

著者:

The Event Horizon Telescope Collaboration

URL:

Abstract:

The Event Horizon Telescope observed the horizon-scale synchrotron emission region around the Galactic center supermassive black hole, Sagittarius A$^\ast$ (Sgr A*), in 2017. These observations revealed a bright, thick ring morphology with a diameter of $51.8\pm 2.3$ µas and modest azimuthal brightness asymmetry, consistent with the expected appearance of a black hole with mass $M \simeq 10^6 $$M_{\odot}$. From these observations, we present the first resolved linear and circular polarimetric images of Sgr A*. The linear polarization images demonstrate that the emission ring is highly polarized, exhibiting a prominent spiral electric vector polarization angle pattern with a peak fractional polarization of $\sim$ 40 % in the western portion of the ring. The circular polarization images feature a modestly ($\sim$ 5 % – 10 %) polarized dipole structure along the emission ring, with negative circular polarization in the western region and positive circular polarization in the eastern region, although our methods exhibit stronger disagreement than for linear polarization. We analyze the data using multiple independent imaging and modeling methods, each of which is validated using a standardized suite of synthetic data sets. While the detailed spatial distribution of the linear polarization along the ring remains uncertain owing to the intrinsic variability of the source, the spiraling polarization structure is robust to methodological choices. The degree and orientation of the linear polarization provide stringent constraints for the black hole and its surrounding magnetic fields, which we discuss in an accompanying publication.

First Sagittarius A$^\ast$ Event Horizon Telescope Results. VIII. Physical Interpretation of the Polarized Ring

Fri, 01 Mar 2024 00:00:00 +0000

The Astrophysical Journal Letters, vol. 964, no. 2, pp. L26(37pp)

著者:

The Event Horizon Telescope Collaboration

URL:

Abstract:

In a companion paper, we present the first spatially resolved polarized image of Sagittarius A* on event horizon scales, captured using the Event Horizon Telescope, a global very long baseline interferometric array operating at a wavelength of 1.3 mm. Here we interpret this image using both simple analytic models and numerical general relativistic magnetohydrodynamic (GRMHD) simulations. The large spatially resolved linear polarization fraction (24 % – 28 %, peaking at $\sim$ 40 %) is the most stringent constraint on parameter space, disfavoring models that are too Faraday depolarized. Similar to our studies of M87*, polarimetric constraints reinforce a preference for GRMHD models with dynamically important magnetic fields. Although the spiral morphology of the polarization pattern is known to constrain the spin and inclination angle, the time-variable rotation measure (RM) of Sgr A* (equivalent to $\simeq 46°\pm12°$ rotation at 228 GHz) limits its present utility as a constraint. If we attribute the RM to internal Faraday rotation, then the motion of accreting material is inferred to be counterclockwise, contrary to inferences based on historical polarized flares, and no model satisfies all polarimetric and total intensity constraints. On the other hand, if we attribute the mean RM to an external Faraday screen, then the motion of accreting material is inferred to be clockwise, and one model passes all applied total intensity and polarimetric constraints: a model with strong magnetic fields, a spin parameter of $0.94$, and an inclination of 150°. We discuss how future 345 GHz and dynamical imaging will mitigate our present uncertainties and provide additional constraints on the black hole and its accretion flow.

Ordered magnetic fields around the 3C 84 central black hole

Thu, 01 Feb 2024 00:00:00 +0000

Astronomy & Astrophysics, vol. 682, pp. L3(15pp)

著者:

G. F. Paraschos
J.-Y. Kim
M. Wielgus
J. Röder
T. P. Krichbaum
E. Ros
I. Agudo
I. Myserlis
M. Moscibrodzka
E. Traianou
J. A. Zensus
L. Blackburn
C.-K. Chan
S. Issaoun
M. Janssen
M. D. Johnson
V. L. Fish
The Event Horizon Telescope Collaboration

キーワード:

techniques: high angular resolution
techniques: interferometric
galaxies: active
galaxies: individual: NGC 1275
galaxies: jets

URL:

DOI
arXiv

Abstract:

\em Context. 3C 84 is a nearby radio source with a complex total intensity structure, showing linear polarisation and spectral patterns. A detailed investigation of the central engine region necessitates the use of very-long-baseline interferometry (VLBI) above the hitherto available maximum frequency of 86 GHz. \em Aims. Using ultrahigh resolution VLBI observations at the currently highest available frequency of 228 GHz, we aim to perform a direct detection of compact structures and understand the physical conditions in the compact region of 3C 84. Methods. We used Event Horizon Telescope (EHT) 228 GHz observations and, given the limited $(u,v)$-coverage, applied geometric model fitting to the data. Furthermore, we employed quasi-simultaneously observed, ancillary multi-frequency VLBI data for the source in order to carry out a comprehensive analysis of the core structure. \em Results. We report the detection of a highly ordered, strong magnetic field around the central, supermassive black hole of 3C 84. The brightness temperature analysis suggests that the system is in equipartition. We also determined a turnover frequency of $\nu_{\mathrmm} = (113\pm 4)$ GHz, a corresponding synchrotron self-absorbed magnetic field of $B_{\mathrmSSA}= (2.9 \pm 1.6)$ G, and an equipartition magnetic field of $B_{\mathrmeq} = (5.2 \pm 0.6)$ G. Three components are resolved with the highest fractional polarisation detected for this object ($m_{\mathrmnet}=(17.0\pm 3.9)$ %). The positions of the components are compatible with those seen in low-frequency VLBI observations since 2017–2018. We report a steeply negative slope of the spectrum at 228 GHz. We used these findings to test existing models of jet formation, propagation, and Faraday rotation in 3C 84. \em Conclusions. The findings of our investigation into different flow geometries and black hole spins support an advection-dominated accretion flow in a magnetically arrested state around a rapidly rotating supermassive black hole as a model of the jet-launching system in the core of 3C 84. However, systematic uncertainties due to the limited $(u,v)$-coverage, however, cannot be ignored. Our upcoming work using new EHT data, which offer full imaging capabilities, will shed more light on the compact region of 3C 84.

The Persistent Shadow of the Supermassive Black Hole of M87, I. Observations, calibration, imaging, and analysis

Mon, 01 Jan 2024 00:00:00 +0000

Astronomy & Astrophysics, vol. 681, pp. A79(63pp)

著者:

The Event Horizon Telescope Collaboration

URL:

Abstract:

In April 2019, the Event Horizon Telescope (EHT) Collaboration reported the first-ever event-horizon-scale images of a black hole, resolving the central compact radio source in the giant elliptical galaxy M87. These images reveal a ring with a southerly brightness distribution and a diameter of $\sim$ 42 µas, consistent with the predicted size and shape of a shadow produced by the gravitationally lensed emission around a supermassive black hole. These results were obtained as part of the April 2017 EHT observation campaign, using a global very long baseline interferometric radio array operating at a wavelength of 1.3 mm. Here, we present results based on the second EHT observing campaign, taking place in April 2018 with an improved array, wider frequency coverage, and increased bandwidth. In particular, the additional baselines provided by the Greenland telescope improved the coverage of the array. Multiyear EHT observations provide independent snapshots of the horizon-scale emission, allowing us to confirm the persistence, size, and shape of the black hole shadow, and constrain the intrinsic structural variability of the accretion flow. We have confirmed the presence of an asymmetric ring structure, brighter in the southwest, with a median diameter of $43.3_-3.1^+1.5$ µas. The diameter of the 2018 ring is remarkably consistent with the diameter obtained from the previous 2017 observations. On the other hand, the position angle of the brightness asymmetry in 2018 is shifted by about 30° relative to 2017. The perennial persistence of the ring and its diameter robustly support the interpretation that the ring is formed by lensed emission surrounding a Kerr black hole with a mass $\sim 6.5\times 10^9$ $M_{\odot}$. The significant change in the ring brightness asymmetry implies a spin axis that is more consistent with the position angle of the large-scale jet.

A Search for Pulsars around Sgr A* in the First Event Horizon Telescope Data Set

Wed, 01 Nov 2023 00:00:00 +0000

The Astrophysical Journal, vol. 959, no. 1, pp. 14(27pp)

著者:

Pablo Torne
Kuo Liu
Ralph P. Eatough
Jompoj Wongphechauxsorn
James M. Cordes
Gregory Desvignes
Mariafelicia De Laurentis
Michael Kramer
Scott M. Ransom
Shami Chatterjee
Robert Wharton
Ramesh Karuppusamy
Lindy Blackburn
Michael Janssen
Chi-kwan Chan
Geoffrey, B. Crew
Lynn D. Matthews
Ciriaco Goddi
Helge Rottmann
Jan Wagner
Salvador Sánchez
Ignacio Ruiz
Federico Abbate
Geoffrey C. Bower
Juan J. Salamanca
Arturo I. Gómez-Ruiz
Alfredo Herrera-Aguilar
Wu Jiang
Ru-Sen Lu
Ue-Li Pen
Alexander W. Raymond
Lijing Shao
Zhiqiang Shen
Gabriel Paubert
Miguel Sanchez-Portal
Carsten Kramer
Manuel Castillo
Santiago Navarro
David John
Karl-Friedrich Schuster
Michael D. Johnson
Kazi L. J. Rygl
The Event Horizon Telescope Collaboration

URL:

DOI
arXiv

Abstract:

In 2017 the Event Horizon Telescope (EHT) observed the supermassive black hole at the center of the Milky Way, Sagittarius A$^\ast$ (Sgr A*), at a frequency of 228.1 GHz ($łambda=1.3 mm$). The fundamental physics tests that even a single pulsar orbiting Sgr A* would enable motivate searching for pulsars in EHT data sets. The high observing frequency means that pulsars–which typically exhibit steep emission spectra–are expected to be very faint. However, it also negates pulse scattering, an effect that could hinder pulsar detections in the Galactic center. Additionally, magnetars or a secondary inverse Compton emission could be stronger at millimeter wavelengths than at lower frequencies. We present a search for pulsars close to Sgr A* using the data from the three most sensitive stations in the EHT 2017 campaign: the Atacama Large Millimeter/submillimeter Array, the Large Millimeter Telescope, and the IRAM 30 m Telescope. We apply three detection methods based on Fourier-domain analysis, the fast folding algorithm, and single-pulse searches targeting both pulsars and burst-like transient emission. We use the simultaneity of the observations to confirm potential candidates. No new pulsars or significant bursts were found. Being the first pulsar search ever carried out at such high radio frequencies, we detail our analysis methods and give a detailed estimation of the sensitivity of the search. We conclude that the EHT 2017 observations are only sensitive to a small fraction ($łesssim 2.2 %$) of the pulsars that may exist close to Sgr A*, motivating further searches for fainter pulsars in the region.

First M87 Event Horizon Telescope Results. IX. Detection of Near-horizon Circular Polarization

Wed, 01 Nov 2023 00:00:00 +0000

The Astrophysical Journal Letters, vol. 957, no. 2, pp. L20(42pp)

著者:

The Event Horizon Telescope Collaboration

URL:

DOI
arXiv

Abstract:

Event Horizon Telescope (EHT) observations have revealed a bright ring of emission around the supermassive black hole at the center of the M87 galaxy. EHT images in linear polarization have further identified a coherent spiral pattern around the black hole, produced from ordered magnetic fields threading the emitting plasma. Here we present the first analysis of circular polarization using EHT data, acquired in 2017, which can potentially provide additional insights into the magnetic fields and plasma composition near the black hole. Interferometric closure quantities provide convincing evidence for the presence of circularly polarized emission on event-horizon scales. We produce images of the circular polarization using both traditional and newly developed methods. All methods find a moderate level of resolved circular polarization across the image ($\braket|v|\ge3.7 %$), consistent with the low image-integrated circular polarization fraction measured by the Atacama Large Millimeter/submillimeter Array ($|v_int|\ge 1 %$). Despite this broad agreement, the methods show substantial variation in the morphology of the circularly polarized emission, indicating that our conclusions are strongly dependent on the imaging assumptions because of the limited baseline coverage, uncertain telescope gain calibration, and weakly polarized signal. We include this upper limit in an updated comparison to general relativistic magnetohydrodynamic simulation models. This analysis reinforces the previously reported preference for magnetically arrested accretion flow models. We find that most simulations naturally produce a low level of circular polarization consistent with our upper limit and that Faraday conversion is likely the dominant production mechanism for circular polarization at 230 GHz in M87*.

Polarimetric Geometric Modeling for mm-VLBI Observations of Black Holes

Wed, 01 Nov 2023 00:00:00 +0000

The Astrophysical Journal Letters, vol. 957, no. 2, pp. L21(29pp)

著者:

Freek Roelofs
Michael D. Johnson
Andrew Chael
Michael Janssen
Maciek Wielgus
Avery E. Broderick
The Event Horizon Telescope Collaboration

URL:

DOI
arXiv

Abstract:

The Event Horizon Telescope (EHT) is a millimeter very long baseline interferometry (VLBI) array that has imaged the apparent shadows of the supermassive black holes M87* and Sagittarius A$^\ast$. Polarimetric data from these observations contain a wealth of information on the black hole and accretion flow properties. In this work, we develop polarimetric geometric modeling methods for mm-VLBI data, focusing on approaches that fit data products with differing degrees of invariance to broad classes of calibration errors. We establish a fitting procedure using a polarimetric ``m-ring’’ model to approximate the image structure near a black hole. By fitting this model to synthetic EHT data from general relativistic magnetohydrodynamic models, we show that the linear and circular polarization structure can be successfully approximated with relatively few model parameters. We then fit this model to EHT observations of M87* taken in 2017. In total intensity and linear polarization, the m-ring fits are consistent with previous results from imaging methods. In circular polarization, the m-ring fits indicate the presence of event-horizon-scale circular polarization structure, with a persistent dipolar asymmetry and orientation across several days. The same structure was recovered independently of observing band, used data products, and model assumptions. Despite this broad agreement, imaging methods do not produce similarly consistent results. Our circular polarization results, which imposed additional assumptions on the source structure, should thus be interpreted with some caution. Polarimetric geometric modeling provides a useful and powerful method to constrain the properties of horizon-scale polarized emission, particularly for sparse arrays like the EHT.

Comparison of Polarized Radiative Transfer Codes Used by the EHT Collaboration

Thu, 01 Jun 2023 00:00:00 +0000

The Astrophysical Journal, vol. 950, no. 1, pp. 35(23pp)

著者:

Ben S. Prather
Jason Dexter
Monika Moscibrodzka
Hung-Yi Pu
Thomas Bronzwaer
Jordy Davelaar
Ziri Younsi
Charles F. Gammie
Roman Gold
George N. Wong
The Event Horizon Telescope Collaboration

URL:

Abstract:

Interpretation of resolved polarized images of black holes by the Event Horizon Telescope (EHT) requires predictions of the polarized emission observable by an Earth-based instrument for a particular model of the black hole accretion system. Such predictions are generated by general relativistic radiative transfer (GRRT) codes, which integrate the equations of polarized radiative transfer in curved spacetime. A selection of ray-tracing GRRT codes used within the EHT Collaboration is evaluated for accuracy and consistency in producing a selection of test images, demonstrating that the various methods and implementations of radiative transfer calculations are highly consistent. When imaging an analytic accretion model, we find that all codes produce images similar within a pixel-wise normalized mean squared error (NMSE) of 0.012 in the worst case. When imaging a snapshot from a cell-based magnetohydrodynamic simulation, we find all test images to be similar within NMSEs of 0.02, 0.04, 0.04, and 0.12 in Stokes I, Q, U, and V, respectively. We additionally find the values of several image metrics relevant to published EHT results to be in agreement to much better precision than measurement uncertainties.

The Event Horizon Telescope Image of the Quasar NRAO 530

Wed, 01 Feb 2023 00:00:00 +0000

The Astrophysical Journal, vol. 943, no. 2, pp. 170(27pp)

著者:

Svetlana Jorstad
Maciek Wielgus
Rocco Lico
Sara Issaoun
Avery E. Broderick
Dominic W. Pesce
Jun Liu
Guang-Yao Zhao
Thomas P. Krichbaum
Lindy Blackburn
Chi-kwan Chan
Michael Janssen
Venkatessh Ramakrishnan
Kazunori Akiyama
Antxon Alberdi
Juan Carlos Algaba
Katherine L. Bouman
Ilje Cho
Antonio Fuentes
José L. Gómez
Mark Gurwell
Michael D. Johnson
Jae-Young Kim
Ru-Sen Lu
Iván Mart{'\i}-Vidal
Monika Moscibrodzka
Felix M. Pötzl
Efthalia Traianou
Ilse van Bemmel
The Event Horizon Telescope Collaboration

URL:

DOI
arXiv

Abstract:

We report on the observations of the quasar NRAO 530 with the Event Horizon Telescope (EHT) on 2017 April 5–7, when NRAO 530 was used as a calibrator for the EHT observations of Sagittarius A$^\ast$. At $z=0.902$, this is the most distant object imaged by the EHT so far. We reconstruct the first images of the source at 230GHz, at an unprecedented angular resolution of $\sim20 µas$, both in total intensity and in linear polarization (LP). We do not detect source variability, allowing us to represent the whole data set with static images. The images reveal a bright feature located on the southern end of the jet, which we associate with the core. The feature is linearly polarized, with a fractional polarization of $\sim$5 % – 8 %, and it has a substructure consisting of two components. Their observed brightness temperature suggests that the energy density of the jet is dominated by the magnetic field. The jet extends over 60µas along a position angle $\sim-28°$. It includes two features with orthogonal directions of polarization (electric vector position angle), parallel and perpendicular to the jet axis, consistent with a helical structure of the magnetic field in the jet. The outermost feature has a particularly high degree of LP, suggestive of a nearly uniform magnetic field. Future EHT observations will probe the variability of the jet structure on microarcsecond scales, while simultaneous multiwavelength monitoring will provide insight into the high-energy emission origin.

Blind Deconvolution with Non-smooth Regularization via Bregman Proximal DCAs

Sun, 01 Jan 2023 00:00:00 +0000

Signal Processing, vol. 202, pp. 108734(9pp)

著者:

Shota Takahashi
Mirai Tanaka
Shiro Ikeda

キーワード:

optimization
Bregman divergence
proximal DC algorithm

URL:

DOI
arXiv

Abstract:

Blind deconvolution is a technique to recover an original signal without knowing a convolving filter. It is naturally formulated as a minimization of a quartic objective function under some assumption. Because its differentiable part does not have a Lipschitz continuous gradient, existing first-order methods are not theoretically supported. In this paper, we employ the Bregman-based proximal methods, whose convergence is theoretically guaranteed under the $L$-smooth adaptable ($L$-smad) property. We first reformulate the objective function as a difference of convex (DC) functions and apply the Bregman proximal DC algorithm (BPDCA). This DC decomposition satisfies the $L$-smad property. The method is extended to the BPDCA with extrapolation (BPDCAe) for faster convergence. When our regularizer has a sufficiently simple structure, each iteration is solved in a closed-form expression, and thus our algorithms solve large-scale problems efficiently. We also provide the stability analysis of the equilibriums and demonstrate the proposed methods through numerical experiments on image deblurring. The results show that BPDCAe successfully recovered the original image and outperformed other existing algorithms.

Resolving the Inner Parsec of the Blazar J1924–2914 with the Event Horizon Telescope

Mon, 01 Aug 2022 00:00:00 +0000

The Astrophysical Journal, vol. 934, no. 2, pp. 145(21pp)

著者:

Sara Issaoun
Maciek Wielgus
Svetlana Jorstad
Thomas P. Krichbaum
Lindy Blackburn
Michael Janssen
Chi-Kwan Chan
Dominic W. Pesce
José L. Gómez
Kazunori Akiyama
Monika Mo'scibrodzka
Iván Mart{'\i}-Vidal
Andrew Chael
Rocco Lico
Jun Liu
Venkatessh Ramakrishnan
Mikhail Lisakov
Antonio Fuentes
Guang-Yao Zhao
Kotaro Moriyama
Avery E. Broderick
Paul Tiede
Nicholas R. MacDonald
Yosuke Mizuno
Efthalia Traianou
Laurent Loinard
Jordy Davelaar
Mark Gurwell
Ru-Sen Lu
The Event Horizon Telescope Collaboration

URL:

Abstract:

The blazar J1924–2914 is a primary Event Horizon Telescope (EHT) calibrator for the Galactic center’s black hole Sagittarius A$âst$. Here we present the first total and linearly polarized intensity images of this source obtained with the unprecedented 20 µas resolution of the EHT. J1924–2914 is a very compact flat-spectrum radio source with strong optical variability and polarization. In April 2017 the source was observed quasi-simultaneously with the EHT (April 5–11), the Global Millimeter VLBI Array (April 3), and the Very Long Baseline Array (April 28), giving a novel view of the source at four observing frequencies, 230, 86, 8.7, and 2.3 GHz. These observations probe jet properties from the subparsec to 100 pc scales. We combine the multifrequency images of J1924–2914 to study the source morphology. We find that the jet exhibits a characteristic bending, with a gradual clockwise rotation of the jet projected position angle of about 90° between 2.3 and 230 GHz. Linearly polarized intensity images of J1924–2914 with the extremely fine resolution of the EHT provide evidence for ordered toroidal magnetic fields in the blazar compact core.

天の川銀河中心の巨大ブラックホール Sgr A* の画像化

Mon, 01 Aug 2022 00:00:00 +0000

天文月報, vol. 115, no. 8, pp. 493–494

著者:

森山小太郎
小藤由太郎
池田思朗

URL:

Link

Abstract:

今年Event Horizon Telescope（EHT）によって，我々が住む天の川銀河中心のブラックホールの姿が世界で初めて明らかとなった．本稿ではこの画像がどのように得られたのかを簡単に紹介する．

A Universal Power-law Prescription for Variability from Synthetic Images of Black Hole Accretion Flows

Sun, 01 May 2022 00:00:00 +0000

The Astrophysical Journal Letters, vol. 930, no. 2, pp. L20(32pp)

著者:

Boris Georgiev
Dominic W. Pesce
Avery E. Broderick
George N. Wong
Vedant Dhruv
Maciek Wielgus
Charles F. Gammie
Chi-Kwan Chan
Koushik Chatterjee
Razieh Emami
Yosuke Mizuno
Roman Gold
Christian M. Fromm
Angelo Ricarte
Doosoo Yoon
Abhishek V. Joshi
Ben Prather
Alejandro Cruz-Osorio
Michael D. Johnson
Oliver Porth
Héctor Olivares
Ziri Younsi
Luciano Rezzolla
Jesse Vos
Richard Qiu
Antonios Nathanail
Ramesh Narayan
Andrew Chael
Richard Anantua
Monika Moscibrodzka
The Event Horizon Telescope Collaboration

URL:

Abstract:

We present a framework for characterizing the spatiotemporal power spectrum of the variability expected from the horizon-scale emission structure around supermassive black holes, and we apply this framework to a library of general relativistic magnetohydrodynamic (GRMHD) simulations and associated general relativistic ray-traced images relevant for Event Horizon Telescope (EHT) observations of Sgr A*.Wefind that the variability power spectrum is generically a red-noise process in both the temporal and spatial dimensions, with the peak in power occurring on the longest timescales and largest spatial scales. When both the time-averaged source structure and the spatially integrated light-curve variability are removed, the residual power spectrum exhibits a universal broken power-law behavior. On small spatial frequencies, the residual power spectrum rises as the square of the spatial frequency and is proportional to the variance in the centroid of emission. Beyond some peak in variability power, the residual power spectrum falls as that of the time-averaged source structure, which is similar across simulations; this behavior can be naturally explained if the variability arises from a multiplicative random field that has a steeper high-frequency power-law index than that of the time-averaged source structure. We briefly explore the ability of power spectral variability studies to constrain physical parameters relevant for the GRMHD simulations, which can be scaled to provide predictions for black holes in a range of systems in the optically thin regime. We present specific expectations for the behavior of the M87* and Sgr A* accretion flows as observed by the EHT.

Characterizing and Mitigating Intraday Variability: Reconstructing Source Structure in Accreting Black Holes with mm-VLBI

Sun, 01 May 2022 00:00:00 +0000

The Astrophysical Journal Letters, vol. 930, no. 2, pp. L21(30pp)

著者:

Avery E. Broderick
Roman Gold
Boris Georgiev
Dominic W. Pesce
Paul Tiede
Chunchong Ni
Kotaro Moriyama
The Event Horizon Telescope Collaboration

URL:

Abstract:

The extraordinary physical resolution afforded by the Event Horizon Telescope has opened a window onto the astrophysical phenomena unfolding on horizon scales in two known black holes, M87* and Sgr A*. However, with this leap in resolution has come a new set of practical complications. Sgr A* exhibits intraday variability that violates the assumptions underlying Earth aperture synthesis, limiting traditional image reconstruction methods to short timescales and data sets with very sparse $(u,v)$ coverage. We present a new set of tools to detect and mitigate this variability. We develop a data-driven, model-agnostic procedure to detect and characterize the spatial structure of intraday variability. This method is calibrated against a large set of mock data sets, producing an empirical estimator of the spatial power spectrum of the brightness fluctuations. We present a novel Bayesian noise modeling algorithm that simultaneously reconstructs an average image and statistical measure of the fluctuations about it using a parameterized form for the excess variance in the complex visibilities not otherwise explained by the statistical errors. These methods are validated using a variety of simulated data, including general relativistic magnetohydrodynamic simulations appropriate for Sgr A* and M87*. We find that the reconstructed source structure and variability are robust to changes in the underlying image model. We apply these methods to the 2017 EHT observations of M87*, finding evidence for variability across the EHT observing campaign. The variability mitigation strategies presented are widely applicable to very long baseline interferometry observations of variable sources generally, for which they provide a data-informed averaging procedure and natural characterization of inter-epoch image consistency.

First Sagittarius A$^\ast$ Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky Way

Sun, 01 May 2022 00:00:00 +0000

The Astrophysical Journal Letters, vol. 930, no. 2, pp. L12(21pp)

著者:

The Event Horizon Telescope Collaboration

URL:

DOI
arXiv

Abstract:

We present the first Event Horizon Telescope (EHT) observations of Sagittarius A$^\ast$ (Sgr A*), the Galactic center source associated with a supermassive black hole. These observations were conducted in 2017 using a global interferometric array of eight telescopes operating at a wavelength of $łambda=1.3 mm$. The EHT data resolve a compact emission region with intrahour variability. A variety of imaging and modeling analyses all support an image that is dominated by a bright, thick ring with a diameter of $51.8\pm 2.3 µas$ (68 % credible interval). The ring has modest azimuthal brightness asymmetry and a comparatively dim interior. Using a large suite of numerical simulations, we demonstrate that the EHT images of Sgr A* are consistent with the expected appearance of a Kerr black hole with mass $\sim 4\times 10^6$ $M_{\odot}$, which is inferred to exist at this location based on previous infrared observations of individual stellar orbits, as well as maser proper-motion studies. Our model comparisons disfavor scenarios where the black hole is viewed at high inclination ($i>50°$), as well as nonspinning black holes and those with retrograde accretion disks. Our results provide direct evidence for the presence of a supermassive black hole at the center of the Milky Way, and for the first time we connect the predictions from dynamical measurements of stellar orbits on scales of 103–105 gravitational radii to event-horizon-scale images and variability. Furthermore, a comparison with the EHT results for the supermassive black hole M87* shows consistency with the predictions of general relativity spanning over three orders of magnitude in central mass.

First Sagittarius A$^\ast$ Event Horizon Telescope Results. II. EHT and Multiwavelength Observations, Data Processing, and Calibration

Sun, 01 May 2022 00:00:00 +0000

The Astrophysical Journal Letters, vol. 930, no. 2, pp. L13(31pp)

著者:

The Event Horizon Telescope Collaboration

URL:

DOI
arXiv

Abstract:

We present Event Horizon Telescope (EHT) 1.3 mm measurements of the radio source located at the position of the supermassive black hole Sagittarius A$^\ast$ (Sgr A*), collected during the 2017 April 5–11 campaign. The observations were carried out with eight facilities at six locations across the globe. Novel calibration methods are employed to account for Sgr A*’s flux variability. The majority of the 1.3 mm emission arises from horizon scales, where intrinsic structural source variability is detected on timescales of minutes to hours. The effects of interstellar scattering on the image and its variability are found to be subdominant to intrinsic source structure. The calibrated visibility amplitudes, particularly the locations of the visibility minima, are broadly consistent with a blurred ring with a diameter of $\sim50 µas$, as determined in later works in this series. Contemporaneous multiwavelength monitoring of Sgr A* was performed at 22, 43, and 86 GHz and at near-infrared and X-ray wavelengths. Several X-ray flares from Sgr A* are detected by Chandra, one at low significance jointly with Swift on 2017 April 7 and the other at higher significance jointly with NuSTAR on 2017 April 11. The brighter April 11 flare is not observed simultaneously by the EHT but is followed by a significant increase in millimeter flux variability immediately after the X-ray outburst, indicating a likely connection in the emission physics near the event horizon. We compare Sgr A*’s broadband flux during the EHT campaign to its historical spectral energy distribution and find that both the quiescent emission and flare emission are consistent with its long-term behavior.

First Sagittarius A$^\ast$ Event Horizon Telescope Results. III. Imaging of the Galactic Center Supermassive Black Hole

Sun, 01 May 2022 00:00:00 +0000

The Astrophysical Journal Letters, vol. 930, no. 2, pp. L14(64pp)

著者:

The Event Horizon Telescope Collaboration

URL:

DOI
arXiv

Abstract:

We present the first event-horizon-scale images and spatiotemporal analysis of Sgr A* taken with the Event Horizon Telescope in 2017 April at a wavelength of 1.3 mm. Imaging of Sgr A* has been conducted through surveys over a wide range of imaging assumptions using the classical CLEAN algorithm, regularized maximum likelihood methods, and a Bayesian posterior sampling method. Different prescriptions have been used to account for scattering effects by the interstellar medium toward the Galactic center. Mitigation of the rapid intraday variability that characterizes Sgr A* has been carried out through the addition of a variability noise budget'' in the observed visibilities, facilitating the reconstruction of static full-track images. Our static reconstructions of Sgr A* can be clustered into four representative morphologies that correspond to ring images with three different azimuthal brightness distributions and a small cluster that contains diverse nonring morphologies. Based on our extensive analysis of the effects of sparse $(u, v)$-coverage, source variability, and interstellar scattering, as well as studies of simulated visibility data, we conclude that the Event Horizon Telescope Sgr A* data show compelling evidence for an image that is dominated by a bright ring of emission with a ring diameter of $\sim 50 µas$, consistent with the expected shadow’’ of a $4\times 10^6$ $M_{\odot}$ black hole in the Galactic center located at a distance of 8 k pc.

First Sagittarius A$^\ast$ Event Horizon Telescope Results. IV. Variability, Morphology, and Black Hole Mass

Sun, 01 May 2022 00:00:00 +0000

The Astrophysical Journal Letters, vol. 930, no. 2, pp. L15(52pp)

著者:

The Event Horizon Telescope Collaboration

URL:

DOI
arXiv

Abstract:

In this paper we quantify the temporal variability and image morphology of the horizon-scale emission from Sgr A*, as observed by the EHT in 2017 April at a wavelength of 1.3 mm. We find that the Sgr A* data exhibit variability that exceeds what can be explained by the uncertainties in the data or by the effects of interstellar scattering. The magnitude of this variability can be a substantial fraction of the correlated flux density, reaching $\sim100 %$ on some baselines. Through an exploration of simple geometric source models, we demonstrate that ringlike morphologies provide better fits to the Sgr A* data than do other morphologies with comparable complexity. We develop two strategies for fitting static geometric ring models to the time-variable Sgr A* data; one strategy fits models to short segments of data over which the source is static and averages these independent fits, while the other fits models to the full data set using a parametric model for the structural variability power spectrum around the average source structure. Both geometric modeling and image-domain feature extraction techniques determine the ring diameter to be $51.8\pm2.3 µas$ (68 % credible intervals), with the ring thickness constrained to have an FWHM between $\sim30 %$ and 50 % of the ring diameter. To bring the diameter measurements to a common physical scale, we calibrate them using synthetic data generated from GRMHD simulations. This calibration constrains the angular size of the gravitational radius to be $4.8_-0.7^+1.4$ µas, which we combine with an independent distance measurement from maser parallaxes to determine the mass of Sgr A* to be $4.0_-0.6^+1.1\times 10^6$ $M_{\odot}$.

First Sagittarius A$^\ast$ Event Horizon Telescope Results. V. Testing Astrophysical Models of the Galactic Center Black Hole

Sun, 01 May 2022 00:00:00 +0000

The Astrophysical Journal Letters, vol. 930, no. 2, pp. L16(49pp)

著者:

The Event Horizon Telescope Collaboration

URL:

DOI
arXiv

Abstract:

In this paper we provide a first physical interpretation for the Event Horizon Telescope’s (EHT) 2017 observations of Sgr A*. Our main approach is to compare resolved EHT data at 230 GHz and unresolved non-EHT observations from radio to X-ray wavelengths to predictions from a library of models based on time-dependent general relativistic magnetohydrodynamics simulations, including aligned, tilted, and stellar-wind-fed simulations; radiative transfer is performed assuming both thermal and nonthermal electron distribution functions. We test the models against 11 constraints drawn from EHT 230 GHz data and observations at 86 GHz, 2.2 µm, and in the X-ray. All models fail at least one constraint. Light-curve variability provides a particularly severe constraint, failing nearly all strongly magnetized (magnetically arrested disk (MAD)) models and a large fraction of weakly magnetized models. A number of models fail only the variability constraints. We identify a promising cluster of these models, which are MAD and have inclination $iłe 30°$. They have accretion rate $(5.2-9.5) \times 10^-9$ $M_{\odot}$ yr$^-1$, bolometric luminosity $(6.8-9.2) \times 1035$ erg s$^-1$, and outflow power $(1.3-4.8) \times 1038$ erg s$^-1$. We also find that all models with $i \ge \arg70$ fail at least two constraints, as do all models with equal ion and electron temperature; exploratory, nonthermal model sets tend to have higher 2.2 µm flux density; and the population of cold electrons is limited by X-ray constraints due to the risk of bremsstrahlung overproduction. Finally, we discuss physical and numerical limitations of the models, highlighting the possible importance of kinetic effects and duration of the simulations.

First Sagittarius A$^\ast$ Event Horizon Telescope Results. VI. Testing the Black Hole Metric

Sun, 01 May 2022 00:00:00 +0000

The Astrophysical Journal Letters, vol. 930, no. 2, pp. L17(44pp)

著者:

The Event Horizon Telescope Collaboration

URL:

DOI
arXiv

Abstract:

Astrophysical black holes are expected to be described by the Kerr metric. This is the only stationary, vacuum, axisymmetric metric, without electromagnetic charge, that satisfies Einstein’s equations and does not have pathologies outside of the event horizon. We present new constraints on potential deviations from the Kerr prediction based on 2017 EHT observations of Sagittarius A$^\ast$ (Sgr A*). We calibrate the relationship between the geometrically defined black hole shadow and the observed size of the ring-like images using a library that includes both Kerr and non-Kerr simulations. We use the exquisite prior constraints on the mass-to-distance ratio for Sgr A* to show that the observed image size is within $\sim10 %$ of the Kerr predictions. We use these bounds to constrain metrics that are parametrically different from Kerr, as well as the charges of several known spacetimes. To consider alternatives to the presence of an event horizon, we explore the possibility that Sgr A* is a compact object with a surface that either absorbs and thermally reemits incident radiation or partially reflects it. Using the observed image size and the broadband spectrum of Sgr A*, we conclude that a thermal surface can be ruled out and a fully reflective one is unlikely. We compare our results to the broader landscape of gravitational tests. Together with the bounds found for stellar-mass black holes and the M87 black hole, our observations provide further support that the external spacetimes of all black holes are described by the Kerr metric, independent of their mass.

Millimeter Light Curves of Sagittarius A$^\ast$ Observed during the 2017 Event Horizon Telescope Campaign

Sun, 01 May 2022 00:00:00 +0000

The Astrophysical Journal Letters, vol. 930, no. 2, pp. L19(32pp)

著者:

Maciek Wielgus
Nicola Marchili
Iván Mart{'\i}-Vidal
Garrett K. Keating
Venkatessh Ramakrishnan
Paul Tiede
Ed Fomalont
Sara Issaoun
Joey Neilsen
Michael A. Nowak
Lindy Blackburn
Charles F. Gammie
Ciriaco Goddi
Daryl Haggard
Daeyoung Lee
Monika Moscibrodzka
Alexandra J. Tetarenko
Geoffrey C. Bower
Chi-Kwan Chan
Koushik Chatterjee
Paul M. Chesler
Jason Dexter
Sheperd S. Doeleman
Boris Georgiev
Mark Gurwell
Michael D. Johnson
Daniel P. Marrone
Alejandro Mus
Dimitrios Psaltis
Bart Ripperda
Gunther Witzel
The Event Horizon Telescope Collaboration

URL:

Abstract:

The Event Horizon Telescope (EHT) observed the compact radio source, Sagittarius A$^\ast$ (Sgr A*), in the Galactic Center on 2017 April 5–11 in the 1.3 mm wavelength band. At the same time, interferometric array data from the Atacama Large Millimeter/submillimeter Array and the Submillimeter Array were collected, providing Sgr A* light curves simultaneous with the EHT observations. These data sets, complementing the EHT very long baseline interferometry, are characterized by a cadence and signal-to-noise ratio previously unattainable for Sgr A* at millimeter wavelengths, and they allow for the investigation of source variability on timescales as short as a minute. While most of the light curves correspond to a low variability state of Sgr A*, the April 11 observations follow an X-ray flare and exhibit strongly enhanced variability. All of the light curves are consistent with a red-noise process, with a power spectral density (PSD) slope measured to be between $-2$ and $-3$ on timescales between 1 minute and several hours. Our results indicate a steepening of the PSD slope for timescales shorter than 0.3 hr. The spectral energy distribution is flat at 220 GHz, and there are no time lags between the 213 and 229 GHz frequency bands, suggesting low optical depth for the event horizon scale source. We characterize Sgr A*’s variability, highlighting the different behavior observed just after the X-ray flare, and use Gaussian process modeling to extract a decorrelation timescale and a PSD slope. We also investigate the systematic calibration uncertainties by analyzing data from independent data reduction pipelines.

Selective Dynamical Imaging of Interferometric Data

Sun, 01 May 2022 00:00:00 +0000

The Astrophysical Journal Letters, vol. 930, no. 2, pp. L18(21pp)

著者:

Joseph Farah
Peter Galison
Kazunori Akiyama
Katherine L. Bouman
Geoffrey C. Bower
Andrew Chael
Antonio Fuentes
José L. Gómez
Mareki Honma
Michael D. Johnson
Yutaro Kofuji
Daniel P. Marrone
Kotaro Moriyama
Ramesh Narayan
Dominic W. Pesce
Paul Tiede
Maciek Wielgus
Guang-Yao Zhao
T
The Event Horizon Telescope Collaboration

URL:

Abstract:

Recent developments in very long baseline interferometry (VLBI) have made it possible for the Event Horizon Telescope (EHT) to resolve the innermost accretion flows of the largest supermassive black holes on the sky. The sparse nature of the EHT’s $(u,v)$-coverage presents a challenge when attempting to resolve highly time-variable sources. We demonstrate that the changing $(u,v)$-coverage of the EHT can contain regions of time over the course of a single observation that facilitate dynamical imaging. These optimal time regions typically have projected baseline distributions that are approximately angularly isotropic and radially homogeneous. We derive a metric of coverage quality based on baseline isotropy and density that is capable of ranking array configurations by their ability to produce accurate dynamical reconstructions. We compare this metric to existing metrics in the literature and investigate their utility by performing dynamical reconstructions on synthetic data from simulated EHT observations of sources with simple orbital variability. We then use these results to make recommendations for imaging the 2017 EHT Sgr A* data set.

The Variability of the Black Hole Image in M87 at the Dynamical Timescale

Sat, 01 Jan 2022 00:00:00 +0000

The Astrophysical Journal, vol. 925, no. 1, pp. 13(19pp)

著者:

Kaushik Satapathy
Dimitrios Psaltis
Feryal Özel
Lia Medeiros
Sean T. Dougall
Chi-Kwan Chan
Maciek Wielgus
Ben S. Prather
George N. Wong
Charles F. Gammie
The Event Horizon Telescope Collaboration

URL:

DOI
arXiv

Abstract:

The black hole images obtained with the Event Horizon Telescope (EHT) are expected to be variable at the dynamical timescale near their horizons. For the black hole at the center of the M87 galaxy, this timescale (5–61 days) is comparable to the 6 day extent of the 2017 EHT observations. Closure phases along baseline triangles are robust interferometric observables that are sensitive to the expected structural changes of the images but are free of station-based atmospheric and instrumental errors. We explored the day-to-day variability in closure-phase measurements on all six linearly independent nontrivial baseline triangles that can be formed from the 2017 observations. We showed that three triangles exhibit very low day-to-day variability, with a dispersion of $\sim 3°$ – 5°. The only triangles that exhibit substantially higher variability ($\sim 90°$ – 180°) are the ones with baselines that cross the visibility amplitude minima on the $u-v$ plane, as expected from theoretical modeling. We used two sets of general relativistic magnetohydrodynamic simulations to explore the dependence of the predicted variability on various black hole and accretion-flow parameters. We found that changing the magnetic field configuration, electron temperature model, or black hole spin has a marginal effect on the model consistency with the observed level of variability. On the other hand, the most discriminating image characteristic of models is the fractional width of the bright ring of emission. Models that best reproduce the observed small level of variability are characterized by thin ring-like images with structures dominated by gravitational lensing effects and thus least affected by turbulence in the accreting plasmas.

ALMA Super-resolution Imaging of T Tau: $r = 12$ au Gap in the Compact Dust Disk around T Tau N

Wed, 01 Dec 2021 00:00:00 +0000

The Astrophysical Journal, vol. 923, no. 1, pp. 121

著者:

Masayuki Yamaguchi
Takashi Tsukagoshi
Takayuki Muto
Hideko Nomura
Takeshi Nakazato
Shiro Ikeda
Motohide Tamura
Ryohei Kawabe

キーワード:

ALMA
radio interferometer
protoplanetary disk

URL:

DOI
arXiv

Abstract:

Based on Atacama Large Millimeter/submillimeter Array (ALMA) observations, compact protoplanetary disks with dust radii of $r łesssim 20 - 40 au$ were found to be dominant in nearby low-mass star formation regions. However, their substructures have not been investigated because of the limited spatial resolution achieved so far. We apply a newly developed super-resolution imaging technique utilizing sparse modeling (SpM) to explore several au-scale structures in such compact disks. SpM imaging can directly solve for the incomplete sampling of visibilities in the spatial frequency and potentially improve the fidelity and effective spatial resolution of ALMA images. Here we present the results of the application to the T Tau system. We use the ALMA 1.3 mm continuum data and achieve an effective spatial resolution of $\sim30 %$ (5 au) compared with the conventional CLEAN beam size at a resolution of 17 au. The reconstructed image reveals a new annular gap structure at $r = 12 au$ in the T Tau N compact disk, with a dust radius of 24 au, and resolves the T Tau Sa and Sb binary into two sources. If the observed gap structure in the T Tau N disk is caused by an embedded planet, we estimate a Saturn-mass planet when the viscous parameter of the disk is $10^-3$. Ultimately, ALMA observations with enough angular resolution and sensitivity should be able to verify the consistency of the super-resolution imaging and definitely confirm the existence of this disk substructure.

A Data-scientific Noise-removal Method for Efficient Submillimeter Spectroscopy With Single-dish Telescopes

Sun, 01 Aug 2021 00:00:00 +0000

The Astronomical Journal, vol. 162, no. 3, pp. 111

著者:

Akio Taniguchi
Yoichi Tamura
Shiro Ikeda
Tatsuya Takekoshi
Ryohei Kawabe

キーワード:

optimization
Bregman divergence
proximal DC algorithm

URL:

DOI
arXiv

Abstract:

For submillimeter spectroscopy with ground-based single-dish telescopes, removing the noise contribution from the Earth’s atmosphere and the instrument is essential. For this purpose, here we propose a new method based on a data-scientific approach. The key technique is statistical matrix decomposition that automatically separates the signals of astronomical emission lines from the drift noise components in the fast-sampled ($1 - 10 Hz$) time-series spectra obtained by a position-switching (PSW) observation. Because the proposed method does not apply subtraction between two sets of noisy data (i.e., on-source and off-source spectra), it improves the observation sensitivity by a factor of $\sqrt2$. It also reduces artificial signals such as baseline ripples on a spectrum, which may also help to improve the effective sensitivity. We demonstrate this improvement by using the spectroscopic data of emission lines toward a high-redshift galaxy observed with a 2 mm receiver on the 50 m Large Millimeter Telescope. Since the proposed method is carried out offline and no additional measurements are required, it offers an instant improvement on the spectra reduced so far with the conventional method. It also enables efficient deep spectroscopy driven by the future 50 m class large submillimeter single-dish telescopes, where fast PSW observations by mechanical antenna or mirror drive are difficult to achieve.

Event Horizon Telescope observations of the jet launching and collimation in Centaurus A

Thu, 01 Jul 2021 00:00:00 +0000

Nature Astronomy, vol. 5, pp. 1017–1028

著者:

M. Janssen
H. Falcke
M. Kadler
Eduardo Ros
Maciek Wielgus
Kazunori Akiyama
Mislav Balokovi'c
Lindy Blackburn
Katherine L. Bouman
Andrew Chael
Chi-Kwan Chan
Koushik Chatterjee
Jordy Davelaar
Philip G. Edwards
Christian M. Fromm
José L. Gómez
Ciriaco Goddi
Sara Issaoun
Michael D. Johnson
Junhan Kim
Jun Yi Koay
Thomas P. Krichbaum
Jun Liu
Elisabetta Liuzzo
Sera Markoff
Alex Markowitz
Daniel P. Marrone
Yosuke Mizuno
Cornelia Müller
Chunchong Ni
Dominic W. Pesce
Venkatessh Ramakrishnan
Freek Roelofs
Kazi L. J. Rygl
Ilse van Bemmel
The Event Horizon Telescope Collaboration

URL:

Abstract:

Very-long-baseline interferometry (VLBI) observations of active galactic nuclei at millimetre wavelengths have the power to reveal the launching and initial collimation region of extragalactic radio jets, down to 10$-$100 gravitational radii ($r_g\equiv GM/c^2$) scales in nearby sources. Centaurus A is the closest radio-loud source to Earth. It bridges the gap in mass and accretion rate between the supermassive black holes (SMBHs) in Messier 87 and our Galactic Centre. A large southern declination of $-43°$ has, however, prevented VLBI imaging of Centaurus A below a wavelength of 1 cm thus far. Here we show the millimetre VLBI image of the source, which we obtained with the Event Horizon Telescope at 228 GHz. Compared with previous observations, we image the jet of Centaurus A at a tenfold higher frequency and sixteen times sharper resolution and thereby probe sub-lightday structures. We reveal a highly collimated, asymmetrically edge-brightened jet as well as the fainter counterjet. We find that the source structure of Centaurus A resembles the jet in Messier 87 on $\sim$500 $r_g$ scales remarkably well. Furthermore, we identify the location of Centaurus A’s SMBH with respect to its resolved jet core at a wavelength of 1.3 mm and conclude that the source’s event horizon shadow should be visible at terahertz frequencies. This location further supports the universal scale invariance of black holes over a wide range of masses.

Three-dimensional Reconstruction of Weak-lensing Mass Maps with a Sparsity Prior. I. Cluster Detection

Thu, 01 Jul 2021 00:00:00 +0000

The Astrophysical Journal, vol. 916, no. 2, pp. 67(13pp)

著者:

Xiangchong Li
Naoki Yoshida
Masamune Oguri
Shiro Ikeda
Wentao Luo

キーワード:

weak-lensing mass maps
sparse modeling

URL:

DOI
arXiv

Abstract:

We propose a novel method to reconstruct high-resolution three-dimensional mass maps using data from photometric weak-lensing surveys. We apply an adaptive LASSO algorithm to perform a sparsity-based reconstruction on the assumption that the underlying cosmic density field is represented by a sum of Navarro–Frenk–White halos. We generate realistic mock galaxy shear catalogs by considering the shear distortions from isolated halos for the configurations matched to the Subaru Hyper Suprime-Cam Survey with its photometric redshift estimates. We show that the adaptive method significantly reduces line-of-sight smearing that is caused by the correlation between the lensing kernels at different redshifts. Lensing clusters with lower mass limits of $10^14.0$ {h$^-1$$M_{\odot}$}, $10^14.7$ {h$^-1$$M_{\odot}$}, $10^15.0$ {h$^-1$$M_{\odot}$} can be detected with 1.5 \sigma confidence at the low ($z<0.3$), median ($0.3łe z < 0.6$), and high ($0.6 łe z < 0.85$) redshifts, respectively, with an average false detection rate of 0.022 {deg^-2}. The estimated redshifts of the detected clusters are systematically lower than the true values by $\Delta z \sim 0.03$ for halos at $z łe 0.4$, but the relative redshift bias is below 0.5 % for clusters at $0.4 < z łe 0.85$. The standard deviation of the redshift estimation is $0.092$. Our method enables direct three-dimensional cluster detection with accurate redshift estimates.

Extracting common signal components from the X-ray and optical light curves of GX 339-4: new view for anti-correlation

Tue, 01 Jun 2021 00:00:00 +0000

Publications of the Astronomical Society of Japan, vol. 73, no. 3, pp. 716–727

著者:

Tomoki Omama
Makoto Uemura
Shiro Ikeda
Mikio Morii

キーワード:

astrophysics
high energy
signal processing

URL:

DOI
arXiv

Abstract:

Simultaneous X-ray and optical observations of black hole X-ray binaries have shown that the light curves contain multiple correlated and anti-correlated variation components when the objects are in the hard state. In the case of the black hole X-ray binary, GX 339-4, the cross correlation function (CCF) of the light curves suggests a positive correlation with an optical lag of 0.15 s and anti-correlations with an optical lag of 1 s and X-ray lag of 4 s. This indicates the two light curves have some common signal components with different delays. In this study, we extracted and reconstructed those signal components from the data for GX 339-4. The results confirmed that correlation and anti-correlation with the optical lag are two common components. However, we found that the reconstructed light curve for the anti-correlated component indicates a positively correlated variation with an X-ray lag of $\sim+1 s$. In addition, the CCF for this signal component shows anti-correlations not only with the optical lag, but also with the X-ray lag, which is consistent with the CCF for the data. Therefore, our results suggest that the combination of the two positively correlated components, that is, the X-ray preceding signal with the 0.15 s optical lag and the optical preceding signal with the 1 s X-ray lag, can make the observed CCF without anti-correlated signals. The optical preceding signal may be caused by synchrotron emission in a magnetically dominated accretion flow or in a jet, while further study is required to understand the mechanism of the X-ray time lag.

Constraints on black-hole charges with the 2017 EHT observations of M87$^\ast$

Sat, 01 May 2021 00:00:00 +0000

Physical Review D, vol. 103, no. 10, pp. 104047(18pp)

著者:

Prashant Kocherlakota
Luciano Rezzolla
Heino Falcke
Christian M. Fromm
Michael Kramer
Yosuke Mizuno
Antonios Nathanail
Héctor Olivares
Ziri Younsi
The Event Horizon Telescope Collaboration

URL:

Abstract:

Our understanding of strong gravity near supermassive compact objects has recently improved thanks to the measurements made by the Event Horizon Telescope (EHT). We use here the M87* shadow size to infer constraints on the physical charges of a large variety of nonrotating or rotating black holes. For example, we show that the quality of the measurements is already sufficient to rule out that M87* is a highly charged dilaton black hole. Similarly, when considering black holes with two physical and independent charges, we are able to exclude considerable regions of the space of parameters for the doubly-charged dilaton and the Sen black holes.

Noise reduction for weak lensing mass mapping: An application of generative adversarial networks to Subaru Hyper Suprime-Cam first-year data

Thu, 01 Apr 2021 00:00:00 +0000

Monthly Notices of the Royal Astronomical Society, pp. stab982

著者:

Masato Shirasaki
Kana Moriwaki
Taira Oogi
Naoki Yoshida
Shiro Ikeda
Takahiro Nishimichi

キーワード:

cosmology
deep learning
Subaru-HSC

URL:

DOI
arXiv

Abstract:

We propose a deep-learning approach based on generative adversarial networks (GANs) to reduce noise in weak lensing mass maps under realistic conditions. We apply image-to-image translation using conditional GANs to the mass map obtained from the first-year data of Subaru Hyper Suprime-Cam (HSC) survey. We train the conditional GANs by using 25000 mock HSC catalogues that directly incorporate a variety of observational effects. We study the non-Gaussian information in denoised maps using one-point probability distribution functions (PDFs) and also perform matching analysis for positive peaks and massive clusters. An ensemble learning technique with our GANs is successfully applied to reproduce the PDFs of the lensing convergence. About $60\%$ of the peaks in the denoised maps with height greater than 5$\sigma$ have counterparts of massive clusters within a separation of 6 arcmin. We show that PDFs in the denoised maps are not compromised by details of multiplicative biases and photometric redshift distributions, nor by shape measurement errors, and that the PDFs show stronger cosmological dependence compared to the noisy counterpart. We apply our denoising method to a part of the first-year HSC data to show that the observed mass distribution is statistically consistent with the prediction from the standard $Łambda$CDM model.

First M87 Event Horizon Telescope Results. VII. Polarization of the Ring

Mon, 01 Mar 2021 00:00:00 +0000

The Astrophysical Journal Letters, vol. 910, no. 1, pp. L12(48pp)

著者:

The Event Horizon Telescope Collaboration

キーワード:

Event Horizon Telescope
M87

URL:

DOI
arXiv

Abstract:

In 2017 April, the Event Horizon Telescope (EHT) observed the near-horizon region around the supermassive black hole at the core of the M87 galaxy. These 1.3 mm wavelength observations revealed a compact asymmetric ring-like source morphology. This structure originates from synchrotron emission produced by relativistic plasma located in the immediate vicinity of the black hole. Here we present the corresponding linear-polarimetric EHT images of the center of M87. We find that only a part of the ring is significantly polarized. The resolved fractional linear polarization has a maximum located in the southwest part of the ring, where it rises to the level of $\sim 15 %$. The polarization position angles are arranged in a nearly azimuthal pattern. We perform quantitative measurements of relevant polarimetric properties of the compact emission and find evidence for the temporal evolution of the polarized source structure over one week of EHT observations. The details of the polarimetric data reduction and calibration methodology are provided. We carry out the data analysis using multiple independent imaging and modeling techniques, each of which is validated against a suite of synthetic data sets. The gross polarimetric structure and its apparent evolution with time are insensitive to the method used to reconstruct the image. These polarimetric images carry information about the structure of the magnetic fields responsible for the synchrotron emission. Their physical interpretation is discussed in an accompanying publication.

First M87 Event Horizon Telescope Results. VIII. Magnetic Field Structure near The Event Horizon

Mon, 01 Mar 2021 00:00:00 +0000

The Astrophysical Journal Letters, vol. 910, no. 1, pp. L13(43pp)

著者:

The Event Horizon Telescope Collaboration

キーワード:

Event Horizon Telescope
M87

URL:

DOI
arXiv

Abstract:

Event Horizon Telescope (EHT) observations at 230 GHz have now imaged polarized emission around the supermassive black hole in M87 on event-horizon scales. This polarized synchrotron radiation probes the structure of magnetic fields and the plasma properties near the black hole. Here we compare the resolved polarization structure observed by the EHT, along with simultaneous unresolved observations with the Atacama Large Millimeter/submillimeter Array, to expectations from theoretical models. The low fractional linear polarization in the resolved image suggests that the polarization is scrambled on scales smaller than the EHT beam, which we attribute to Faraday rotation internal to the emission region. We estimate the average density $n_e \sim {10^4-7} \per\cubiccm$, magnetic field strength $B \sim 1-30 G$, and electron temperature $T_e \sim (1-12) \times d10 K$ of the radiating plasma in a simple one-zone emission model. We show that the net azimuthal linear polarization pattern may result from organized, poloidal magnetic fields in the emission region. In a quantitative comparison with a large library of simulated polarimetric images from general relativistic magnetohydrodynamic (GRMHD) simulations, we identify a subset of physical models that can explain critical features of the polarimetric EHT observations while producing a relativistic jet of sufficient power. The consistent GRMHD models are all of magnetically arrested accretion disks, where near-horizon magnetic fields are dynamically important. We use the models to infer a mass accretion rate onto the black hole in M87 of $(3-20) \times 10^-4$ $M_{\odot}$ yr$^-1$.

Relationship between radar cross section and optical magnitude based on radar and optical simultaneous observations of faint meteors

Tue, 01 Dec 2020 00:00:00 +0000

Planetary and Space Science, vol. 194, pp. 105011

著者:

Ryou Ohsawa
Akira Hirota
Kohei Morita
Shinsuke Abe
Daniel Kastinen
Johan Kero
Csilla Szasz
Yasunori Fujiwara
Takuji Nakamura
Koji Nishimura
Shigeyuki Sako
Jun-ichi Watanabe
Tsutomu Aoki
Noriaki Arima
Ko Arimatsu
Mamoru Doi
Makoto Ichiki
Shiro Ikeda
Yoshifusa Ita
Toshihiro Kasuga
Naoto Kobayashi
Mitsuru Kokubo
Masahiro Konishi
Hiroyuki Maehara
Noriyuki Matsunaga
Takashi Miyata
Yuki Mori
Mikio Morii
Tomoki Morokuma
Kentaro Motohara
Yoshikazu Nakada
Shin-ichiro Okumura
Yuki Sarugaku
Mikiya Sato
Toshikazu Shigeyama
Takao Soyano
Hidenori Takahashi
Masaomi Tanaka
Ken’ichi Tarusawa
Nozomu Tominaga
Seitaro Urakawa
Fumihiko Usui
Takuya Yamashita
Makoto Yoshikawa

キーワード:

Tomo-e Gozen
Kiso Schmidt Telescope

URL:

DOI
arXiv

Abstract:

Radar and optical simultaneous observations of meteors are important to understand the size distribution of the interplanetary dust. However, faint meteors detected by high power large aperture radar observations, which are typically as faint as 10 mag. In optical, have not been detected until recently in optical observations, mainly due to insufficient sensitivity of the optical observations. In this paper, two radar and optical simultaneous observations were organized. The first observation was carried out in 2009–2010 using Middle and Upper Atmosphere Radar (MU radar) and an image-intensified CCD camera. The second observation was carried out in 2018 using the MU radar and a mosaic CMOS camera, Tomo-e Gozen, mounted on the 1.05 m Kiso Schmidt Telescope. In total, 331 simultaneous meteors were detected. The relationship between radar cross sections and optical V-band magnitudes was well approximated by a linear function. A transformation function from the radar cross section to the V-band magnitude was derived for sporadic meteors. The transformation function was applied to about 150,000 meteors detected by the MU radar in 2009–2015, large part of which are sporadic, and a luminosity function was derived in the magnitude range of $-1.5\sim 9.5 mag$. The luminosity function was well approximated by a single power-law function with the population index of $r=3.52\pm 0.12$. The present observation indicates that the MU radar has capability to detect interplanetary dust of $10^-5$ – $10^0$ g in mass as meteors.

Feature selection for classification of blazars based on optical photometric and polarimetric time-series data

Thu, 01 Oct 2020 00:00:00 +0000

Publications of the Astronomical Society of Japan, vol. 72, no. 5, pp. 74

著者:

Makoto Uemura
Taisei Abe
Yurika Yamada
Shiro Ikeda

キーワード:

classification
model selection

URL:

DOI
arXiv

Abstract:

Blazars can be divided into two subtypes, flat spectrum radio quasars (FSRQs) and BL Lac objects, which have been distinguished phenomenologically by the strength of their optical emission lines, while their physical nature and relationship are still not fully understood. In this paper, we focus on the differences in their variability. We characterize the blazar variability using the Ornstein-Uhlenbeck (OU) process, and investigate the features that are discriminative for the two subtypes. We used optical photometric and polarimetric data obtained with the 1.5 m Kanata telescope for 2008–2014. We found that four features, namely the variation amplitude, characteristic timescale, and non-stationarity of the variability obtained from the light curves and the median of the degree of polarization (PD), are essential for distinguishing between FSRQs and BL Lac objects. FSRQs are characterized by rare and large flares, while the variability of BL Lac objects can be reproduced with a stationary OU process with relatively small amplitudes. The characteristics of the variability are governed not by the differences in the jet structure between the subtypes, but by the peak frequency of the synchrotron emission. This implies that the nature of the variation in the jets is common in FSRQs and BL Lac objects. We found that BL Lac objects tend to have high PD medians, which suggests that they have a stable polarization component. FSRQs have no such component, possibly because of a strong Compton cooling effect in sub-pc scale jets.

Event Horizon Telescope imaging of the archetypal blazar 3C 279 at an extreme 20 microarcsecond resolution

Sat, 01 Aug 2020 00:00:00 +0000

Astronomy & Astrophysics, vol. 640, pp. A69(21pp)

著者:

Jae-Young Kim
Thomas P. Krichbaum
Avery Broderick
Maciek Wielgus
Lindy Blackburn
José L. Gómez
Michael D. Johnson
Katherine L. Bouman
Andrew Chael
Kazunori Akiyama
Svetlana Jorstad
Alan P. Marscher
Sara Issaoun
Michael Janssen
Chi-Kwan Chan
Tuomas Savolainen
Dominic W. Pesce
Feryal Özel
The Event Horizon Telescope Collaboration

URL:

Abstract:

3C 279 is an archetypal blazar with a prominent radio jet that show broadband flux density variability across the entire electromagnetic spectrum. We use an ultra-high angular resolution technique - global Very Long Baseline Interferometry (VLBI) at 1.3 mm (230 GHz) - to resolve the innermost jet of 3C 279 in order to study its fine-scale morphology close to the jet base where highly variable $\gamma$-ray emission is thought to originate, according to various models. The source was observed during four days in April 2017 with the Event Horizon Telescope at 230 GHz, including the phased Atacama Large Millimeter/submillimeter Array (ALMA), at an angular resolution of $\sim$20µas (at a redshift of $z = 0.536$ this corresponds to $\sim 0.13$ pc $\sim$ 1700 Schwarzschild radii with a black hole mass M$_{\mathrmBH}$ $=$ $8\times 10^8$ $M_{\odot}$). Imaging and model-fitting techniques were applied to the data to parameterize the fine-scale source structure and its variation. We find a multicomponent inner jet morphology with the northernmost component elongated perpendicular to the direction of the jet, as imaged at longer wavelengths. The elongated nuclear structure is consistent on all four observing days and across different imaging methods and model-fitting techniques, and therefore appears robust. Owing to its compactness and brightness, we associate the northern nuclear structure as the VLBI ``core’’. This morphology can be interpreted as either a broad resolved jet base or a spatially bent jet. We also find significant day-to-day variations in the closure phases, which appear most pronounced on the triangles with the longest baselines. Our analysis shows that this variation is related to a systematic change of the source structure. Two inner jet components move non-radially at apparent speeds of $\sim$15 c and $\sim$20 c ($\sim$1.3 and $\sim$1.7 µas day$^-1$, respectively), which more strongly supports the scenario of traveling shocks or instabilities in a bent, possibly rotating jet. The observed apparent speeds are also coincident with the 3C 279 large-scale jet kinematics observed at longer (cm) wavelengths, suggesting no significant jet acceleration between the 1.3 mm core and the outer jet. The intrinsic brightness temperature of the jet components are $łesssim1010 K$, a magnitude or more lower than typical values seen at $\ge7 mm$ wavelengths. The low brightness temperature and morphological complexity suggest that the core region of 3C 279 becomes optically thin at short (mm) wavelengths.

Search for Alignment of Disk Orientations in Nearby Star-forming Regions: Lupus, Taurus, Upper Scorpius, $\rho$ Ophiuchi, and Orion

Sat, 01 Aug 2020 00:00:00 +0000

The Astrophysical Journal, vol. 899, no. 1, pp. 55

著者:

Masataka Aizawa
Yasushi Suto
Yoko Oya
Shiro Ikeda
Takeshi Nakazato

キーワード:

ALMA
radio interferometer
protoplanetary disk

URL:

DOI
arXiv

Abstract:

Spatial correlations among protoplanetary disk orientations carry unique information on physics of multiple-star formation processes. We select five nearby star-forming regions that comprise a number of protoplanetary disks with spatially resolved images with ALMA and Hubble Space Telescope, and we search for the mutual alignment of the disk axes. Specifically, we apply the Kuiper test to examine the statistical uniformity of the position angle (PA: the angle of the major axis of the projected disk ellipse measured counterclockwise from the north) distribution. The disks located in the star-forming regions, except the Lupus clouds, do not show any signature of the alignment, supporting the random orientation. Rotational axes of 16 disks with spectroscopic measurement of PA in the Lupus III cloud, a subregion of the Lupus field, however, exhibit a weak and possible departure from the random distribution at a 2 \sigma level, and the inclination angles of the 16 disks are not uniform as well. Furthermore, the mean direction of the disk PAs in the Lupus III cloud is parallel to the direction of its filament structure and approximately perpendicular to the magnetic field direction. We also confirm the robustness of the estimated PAs in the Lupus clouds by comparing the different observations and estimators based on three different methods, including sparse modeling. The absence of the significant alignment of the disk orientation is consistent with the turbulent origin of the disk angular momentum. Further observations are required to confirm/falsify the possible disk alignment in the Lupus III cloud.

ブラックホールシャドウの撮像とデータ科学

Sat, 01 Aug 2020 00:00:00 +0000

数理科学, no. 687, pp. 57–63

著者:

池田思朗

キーワード:

天文データ科学
スパースモデリング
EHT

PRIISM: Python module for Radio Interferometry Imaging with Sparse Modeling

Mon, 01 Jun 2020 00:00:00 +0000

Astrophysics Source Code Library

著者:

Takeshi Nakazato
Shiro Ikeda

キーワード:

ALMA
sparse modeling
radio interferometry
imaging

Abstract:

PRIISM images radio interferometry data using the sparse modeling technique. In addition to generating an image, PRIISM can choose the best image from a range of processing parameters using cross validation. User can obtain statistically optimal images by providing the visibility data with some configuration parameters. The software is implemented as a Python module.

Super-resolution Imaging of the Protoplanetary Disk HD 142527 Using Sparse Modeling

Fri, 01 May 2020 00:00:00 +0000

The Astrophysical Journal, vol. 895, no. 2, pp. 84(14pp)

著者:

Masayuki Yamaguchi
Kazunori Akiyama
Takashi Tsukagoshi
Takayuki Muto
Akimasa Kataoka
Fumie Tazaki
Shiro Ikeda
Misato Fukagawa
Mareki Honma
Ryohei Kawabe

キーワード:

sparse modeling
ALMA
imaging
radio interferometer

URL:

DOI
arXiv

Abstract:

With an emphasis on improving the fidelity even in super-resolution regimes, new imaging techniques have been intensively developed over the last several years, which may provide substantial improvements to the interferometric observation of protoplanetary disks. In this study, sparse modeling (SpM) is applied for the first time to observational data sets taken by the Atacama Large Millimeter/submillimeter Array (ALMA). The two data sets used in this study were taken independently using different array configurations at Band 7 (330 GHz), targeting the protoplanetary disk around HD 142527: one in the shorter-baseline array configuration ($\sim430 m$), and the other in the longer-baseline array configuration ($\sim1570 m$). The image resolutions reconstructed from the two data sets are different by a factor of $\sim$3. We confirm that the previously known disk structures appear on the images produced by both SpM and CLEAN at the standard beam size. The image reconstructed from the shorter-baseline data using the SpM matches that obtained with the longer-baseline data using the CLEAN, achieving a super-resolution image from which a structure finer than the beam size can be reproduced. Our results demonstrate that ongoing intensive development in the SpM imaging technique is beneficial to imaging with ALMA.

SYMBA: An end-to-end VLBI synthetic data generation pipeline - Simulating Event Horizon Telescope observations of M 87

Wed, 01 Apr 2020 00:00:00 +0000

Astronomy & Astrophysics, vol. 636, pp. A5(19pp)

著者:

F. Roelofs
M. Janssen
I. Natarajan
R. Deane
J. Davelaar
H. Olivares
O. Porth
S. N. Paine
K. L. Bouman
R. P. J. Tilanus
I. M. van Bemmel
H. Falcke
The Event Horizon Telescope Collaboration

キーワード:

galaxies: nuclei / black hole physics / telescopes / atmospheric effects / techniques: high angular resolution / techniques: interferometric

URL:

Abstract:

\it Context. Realistic synthetic observations of theoretical source models are essential for our understanding of real observational data. In using synthetic data, one can verify the extent to which source parameters can be recovered and evaluate how various data corruption effects can be calibrated. These studies are the most important when proposing observations of new sources, in the characterization of the capabilities of new or upgraded instruments, and when verifying model-based theoretical predictions in a direct comparison with observational data. \it Aims. We present the SYnthetic Measurement creator for long Baseline Arrays (SYMBA), a novel synthetic data generation pipeline for Very Long Baseline Interferometry (VLBI) observations. SYMBA takes into account several realistic atmospheric, instrumental, and calibration effects. \it Methods. We used SYMBA to create synthetic observations for the Event Horizon Telescope (EHT), a millimetre VLBI array, which has recently captured the first image of a black hole shadow. After testing SYMBA with simple source and corruption models, we study the importance of including all corruption and calibration effects, compared to the addition of thermal noise only. Using synthetic data based on two example general relativistic magnetohydrodynamics (GRMHD) model images of M 87, we performed case studies to assess the image quality that can be obtained with the current and future EHT array for different weather conditions. \it Results. Our synthetic observations show that the effects of atmospheric and instrumental corruptions on the measured visibilities are significant. Despite these effects, we demonstrate how the overall structure of our GRMHD source models can be recovered robustly with the EHT2017 array after performing calibration steps, which include fringe fitting, a priori amplitude and network calibration, and self-calibration. With the planned addition of new stations to the EHT array in the coming years, images could be reconstructed with higher angular resolution and dynamic range. In our case study, these improvements allowed for a distinction between a thermal and a non-thermal GRMHD model based on salient features in reconstructed images.

An optical search for transients lasting a few seconds

Sat, 01 Feb 2020 00:00:00 +0000

Publications of the Astronomical Society of Japan, vol. 72, no. 1, pp. 3

著者:

Michael W. Richmond
Masaomi Tanaka
Tomoki Morokuma
Shigeyuki Sako
Ryou Ohsawa
Noriaki Arima
Nozomu Tominaga
Mamoru Doi
Tsutomu Aoki
Ko Arimatsu
Makoto Ichiki
Shiro Ikeda
Yoshifusa Ita
Toshihiro Kasuga
Koji S. Kawabata
Hideyo Kawakita
Naoto Kobayashi
Mitsuru Kokubo
Masahiro Konishi
Hiroyuki Maehara
Hiroyuki Mito
Takashi Miyata
Yuki Mori
Mikio Morii
Kentaro Motohara
Yoshikazu Nakada
Shin-ichiro Okumura
Hiroki Onozato
Yuki Sarugaku
Mikiya Sato
Toshikazu Shigeyama
Takao Soyano
Hidenori Takahashi
Ataru Tanikawa
Ken’ichi Tarusawa
Seitaro Urakawa
Fumihiko Usui
Junichi Watanabe
Takuya Yamashita
Makoto Yoshikawa

キーワード:

Tomo-e Gozen
Kiso Schmidt Telescope
transient search

URL:

DOI
arXiv

Abstract:

Using a prototype of the Tomo-e Gozen wide-field CMOS mosaic camera, we acquire wide-field optical images at a cadence of 2 Hz and search them for transient sources of duration 1.5 to 11.5 s. Over the course of eight nights, our survey encompasses the equivalent of roughly two days on one square degree, to a fluence equivalent to a limiting magnitude of about $V=15.6$ in a 1 s exposure. After examining by-eye the candidates identified by a software pipeline, we find no sources which meet all our criteria. We compute upper limits to the rate of optical transients consistent with our survey, and compare those to the rates expected and observed for representative sources of ephemeral optical light.

Amino-acid selective isotope labeling enables simultaneous overlapping signal decomposition and information extraction from NMR spectra

Wed, 01 Jan 2020 00:00:00 +0000

Journal of Biomolecular NMR, vol. 74, pp. 125–137

著者:

Takuma Kasai
Shunsuke Ono
Seizo Koshiba
Masayuki Yamamoto
Toshiyuki Tanaka
Shiro Ikeda
Takanori Kigawa

キーワード:

NMR
SiPex
sparse modeling

URL:

Abstract:

Signal overlapping is a major bottleneck for protein NMR analysis. We propose a new method, stable-isotope-assisted parameter extraction (SiPex), to resolve overlapping signals by a combination of amino-acid selective isotope labeling (AASIL) and tensor decomposition. The basic idea of Sipex is that overlapping signals can be decomposed with the help of intensity patterns derived from quantitative fractional AASIL, which also provides amino-acid information. In SiPex, spectra for protein characterization, such as $^15$N relaxation measurements, are assembled with those for amino-acid information to form a four-order tensor, where the intensity patterns from AASIL contribute to high decomposition performance even if the signals share similar chemical shift values or characterization profiles, such as relaxation curves. The loading vectors of each decomposed component, corresponding to an amide group, represent both the amino-acid and relaxation information. This information link provides an alternative protein analysis method that does not require ``assignments’’ in a general sense; i.e., chemical shift determinations, since the amino-acid information for some of the residues allows unambiguous assignment according to the dual selective labeling. SiPex can also decompose signals in time-domain raw data without Fourier transform, even in non-uniformly sampled data without spectral reconstruction. These features of SiPex should expand biological NMR applications by overcoming their overlapping and assignment problems.

New Constraint on the Atmosphere of (50000) Quaoar from a Stellar Occultation

Fri, 01 Nov 2019 00:00:00 +0000

The Astronomical Journal, vol. 158, no. 6, pp. 236

著者:

Ko Arimatsu
Ryou Ohsawa
George L. Hashimoto
Seitaro Urakawa
Jun Takahashi
Miyako Tozuka
Yoichi Itoh
Misato Yamashita
Fumihiko Usui
Tsutomu Aoki
Noriaki Arima
Mamoru Doi
Makoto Ichiki
Shiro Ikeda
Yoshifusa Ita
Toshihiro Kasuga
Naoto Kobayashi
Mitsuru Kokubo
Masahiro Konishi
Hiroyuki Maehara
Noriyuki Matsunaga
Takashi Miyata
Mikio Morii
Tomoki Morokuma
Kentaro Motohara
Yoshikazu Nakada
Shin-ichiro Okumura
Shigeyuki Sako
Yuki Sarugaku
Mikiya Sato
Toshikazu Shigeyama
Takao Soyano
Hidenori Takahashi
Ken’ichi Tarusawa
Nozomu Tominaga
Jun-ichi Watanabe
Takuya Yamashita
Makoto Yoshikawa

URL:

DOI
arXiv

Abstract:

We report observations of a stellar occultation by the classical Kuiper Belt object (50000) Quaoar that occurred on 2019 June 28. A single-chord high-cadence (2Hz) photometry data set was obtained with the Tomo-e Gozen CMOS camera mounted on the 1.05 m Schmidt telescope at Kiso Observatory. The obtained ingress and egress data do not show any indication of atmospheric refraction and allow new 1$\sigma$ and 3$\sigma$ upper limits of 6 and 16 nbar, respectively, to be set for the surface pressure of a pure methane atmosphere. These upper limits are lower than the saturation vapor pressure of methane at Quaoar’s expected mean surface temperature (T$\sim$44 K) and imply the absence of a$\sim$10 nbar-level global atmosphere formed by methane ice on Quaoar’s surface.

A concept for X-ray telescope system with an angular-resolution booster

Tue, 01 Oct 2019 00:00:00 +0000

Publications of the Astronomical Society of Japan, vol. 71, no. 5, pp. 97

著者:

Yoshitomo Maeda
Ryo Iizuka
Takayuki Hayashi
Toshiki Sato
Nozomi Nakaniwa
Mai Takeo
Hitomi Suzuki
Manabu Ishida
Shiro Ikeda
Mikio Morii

URL:

DOI
arXiv

Abstract:

We present a concept for an X-ray imaging system with a high angular resolution and moderate sensitivity. In this concept, a two-dimensional detector, i.e., an imager, is put at a slightly out-of-focus position of the focusing mirror, rather than just at the mirror focus, as in the standard optics, to capture miniature images of objects. In addition, a set of multi-grid masks (or a modulation collimator) is installed in front of the telescope. We find that the masks work as a coded aperture camera and that they boost the angular resolution of the focusing optics. The major advantage of this concept is that a much better angular resolution, having an order of 2–3 or more than in the conventional optics, is achievable, while a high throughput (large effective area) is maintained, which is crucial in photon-limited high-energy astronomy, because any type of mirrors, including lightweight reflective mirrors, can be employed in our concept. If the signal-to-noise ratio is sufficiently high, we estimate that angular resolutions at the diffraction limit of 4’’ and 0.‘‘4 at $\sim$7 keV can be achieved with a pair of masks at distances of 1 m and 100 m, respectively.

Denoising Weak Lensing Mass Maps with Deep Learning

Thu, 01 Aug 2019 00:00:00 +0000

Physical Review D, vol. 100, pp. 043527

著者:

Masato Shirasaki
Naoki Yoshida
Shiro Ikeda

URL:

DOI
arXiv

Abstract:

Weak gravitational lensing is a powerful probe of the large-scale cosmic matter distribution. Widefield galaxy surveys allow us to generate the so-called weak lensing maps, but actual observations suffer from noise due to imperfect measurement of galaxy shape distortions and to the limited number density of the source galaxies. In this paper, we explore a deep-learning approach to reduce the noise. We develop an image-to-image translation method with conditional adversarial networks (CANs), which learn efficient mapping from an input noisy weak lensing map to the underlying noise field. We train the CANs using 30000 image pairs obtained from 1000 ray-tracing simulations of weak gravitational lensing. We show that the trained CANs reproduce the true one-point probability distribution function (PDF) of the noiseless lensing map with a bias less than 1$\sigma$ on average, where $\sigma$ is the statistical error. We perform a Fisher analysis to make forecast for cosmological parameter inference with the one-point lensing PDF. By our denoising method using CANs, the first derivative of the PDF with respect to the cosmic mean matter density and the amplitude of the primordial curvature perturbations becomes larger by $\sim$ 50%. This allows us to improve the cosmological constraints by $\sim$ 30–40% with using observational data from ongoing and upcoming galaxy imaging surveys.

The Event Horizon General Relativistic Magnetohydrodynamic Code Comparison Project

Thu, 01 Aug 2019 00:00:00 +0000

The Astronomical Journal Supplement Series, vol. 243, no. 2, pp. 26(40pp)

著者:

Oliver Porth
Koushik Chatterjee
Ramesh Narayan
Charles F. Gammie
Yosuke Mizuno
Peter Anninos
John G. Baker
Matteo Bugli
Chi-Kwan Chan
Jordy Davelaar
Luca Del Zanna
Zachariah B. Etienne
P. Chris Fragile
Bernard J. Kelly
Matthew Liska
Sera Markoff
Jonathan C. McKinney
Bhupendra Mishra
Scott C. Noble
Hector Olivares
Ben Prather
Luciano Rezzolla
Benjamin R. Ryan
James M. Stone
Niccolo Tomei
Christopher J. White
Ziri Younsi
The Event Horizon Telescope Collaboration

URL:

DOI
arXiv

Abstract:

Recent developments in compact object astrophysics, especially the discovery of merging neutron stars by LIGO, the imaging of the black hole in M87 by the Event Horizon Telescope, and high-precision astrometry of the Galactic Center at close to the event horizon scale by the GRAVITY experiment motivate the development of numerical source models that solve the equations of general relativistic magnetohydrodynamics (GRMHD). Here we compare GRMHD solutions for the evolution of a magnetized accretion flow where turbulence is promoted by the magnetorotational instability from a set of nine GRMHD codes: Athena++, BHAC, Cosmos++, ECHO, H-AMR, iharm3D, HARM-Noble, IllinoisGRMHD, and KORAL. Agreement among the codes improves as resolution increases, as measured by a consistently applied, specially developed set of code performance metrics. We conclude that the community of GRMHD codes is mature, capable, and consistent on these test problems.

The Hyper Suprime-Cam SSP Transient Survey in COSMOS: Overview

Thu, 01 Aug 2019 00:00:00 +0000

Publications of the Astronomical Society of Japan, vol. 71, no. 4, pp. 74

著者:

Naoki Yasuda
Masaomi Tanaka
Nozomu Tominaga
Ji-an Jiang
Takashi J. Moriya
Tomoki Morokuma
Nao Suzuki
Ichiro Takahashi
Masaki S. Yamaguchi
Keiichi Maeda
Masao Sako
Shiro Ikeda
Akisato Kimura
Mikio Morii
Naonori Ueda
Naoki Yoshida
Chien-Hsiu Lee
Sherry H. Suyu
Yutaka Komiyama
Nicolas Regnault
David Rubin

URL:

DOI
arXiv

Abstract:

We present an overview of a deep transient survey of the COSMOS field with the Subaru Hyper Suprime-Cam (HSC). The survey was performed for the 1.77 deg$^2$ ultra-deep layer and 5.78 deg$^2$ deep layer in the Subaru Strategic Program over six- and four-month periods from 2016 to 2017, respectively. The ultra-deep layer reaches a median depth per epoch of 26.4, 26.3, 26.0, 25.6, and 24.6 mag in $g$, $r$, $i$, $z$, and $y$ bands, respectively; the deep layer is $\sim$0.6 mag shallower. In total, 1824 supernova candidates were identified. Based on light-curve fitting and derived light-curve shape parameter, we classified 433 objects as Type Ia supernovae (SNe); among these candidates, 129 objects have spectroscopic or COSMOS2015 photometric redshifts and 58 objects are located at $z > 1$. Our unique data set doubles the number of Type Ia SNe at $z > 1$ and enables various time-domain analyses of Type II SNe, high-redshift superluminous SNe, variable stars, and active galactic nuclei.

First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole

Mon, 01 Apr 2019 00:00:00 +0000

The Astrophysical Journal Letters, vol. 875, no. 1, pp. L1(17pp)

著者:

The Event Horizon Telescope Collaboration

URL:

DOI
arXiv

Abstract:

When surrounded by a transparent emission region, black holes are expected to reveal a dark shadow caused by gravitational light bending and photon capture at the event horizon. To image and study this phenomenon, we have assembled the Event Horizon Telescope, a global very long baseline interferometry array observing at a wavelength of 1.3 mm. This allows us to reconstruct event-horizon-scale images of the supermassive black hole candidate in the center of the giant elliptical galaxy M87. We have resolved the central compact radio source as an asymmetric bright emission ring with a diameter of $42\pm 3 µas$, which is circular and encompasses a central depression in brightness with a flux ratio $\gtrsim 10:1$. The emission ring is recovered using different calibration and imaging schemes, with its diameter and width remaining stable over four different observations carried out in different days. Overall, the observed image is consistent with expectations for the shadow of a Kerr black hole as predicted by general relativity. The asymmetry in brightness in the ring can be explained in terms of relativistic beaming of the emission from a plasma rotating close to the speed of light around a black hole. We compare our images to an extensive library of ray-traced general-relativistic magnetohydrodynamic simulations of black holes and derive a central mass of $M = (6.5\pm 0.7) \times 10^9$ $M_{\odot}$. Our radio-wave observations thus provide powerful evidence for the presence of supermassive black holes in centers of galaxies and as the central engines of active galactic nuclei. They also present a new tool to explore gravity in its most extreme limit and on a mass scale that was so far not accessible.

First M87 Event Horizon Telescope Results. II. Array and Instrumentation

Mon, 01 Apr 2019 00:00:00 +0000

The Astrophysical Journal Letters, vol. 875, no. 1, pp. L2(28pp)

著者:

The Event Horizon Telescope Collaboration

URL:

DOI
arXiv

Abstract:

The Event Horizon Telescope (EHT) is a very long baseline interferometry (VLBI) array that comprises millimeter- and submillimeter-wavelength telescopes separated by distances comparable to the diameter of the Earth. At a nominal operating wavelength of $\sim 1.3 mm$, EHT angular resolution ($łambda/D$) is $\sim 25 µas$, which is sufficient to resolve nearby supermassive black hole candidates on spatial and temporal scales that correspond to their event horizons. With this capability, the EHT scientific goals are to probe general relativistic effects in the strong-field regime and to study accretion and relativistic jet formation near the black hole boundary. In this Letter we describe the system design of the EHT, detail the technology and instrumentation that enable observations, and provide measures of its performance. Meeting the EHT science objectives has required several key developments that have facilitated the robust extension of the VLBI technique to EHT observing wavelengths and the production of instrumentation that can be deployed on a heterogeneous array of existing telescopes and facilities. To meet sensitivity requirements, high-bandwidth digital systems were developed that process data at rates of $64$ gigabit s$^-1$, exceeding those of currently operating cm-wavelength VLBI arrays by more than an order of magnitude. Associated improvements include the development of phasing systems at array facilities, new receiver installation at several sites, and the deployment of hydrogen maser frequency standards to ensure coherent data capture across the array. These efforts led to the coordination and execution of the first Global EHT observations in 2017 April, and to event-horizon-scale imaging of the supermassive black hole candidate in M87.

First M87 Event Horizon Telescope Results. III. Data Processing and Calibration

Mon, 01 Apr 2019 00:00:00 +0000

The Astrophysical Journal Letters, vol. 875, no. 1, pp. L3(32pp)

著者:

The Event Horizon Telescope Collaboration

URL:

DOI
arXiv

Abstract:

We present the calibration and reduction of Event Horizon Telescope (EHT) 1.3 mm radio wavelength observations of the supermassive black hole candidate at the center of the radio galaxy M87 and the quasar 3C 279, taken during the 2017 April 5–11 observing campaign. These global very long baseline interferometric observations include for the first time the highly sensitive Atacama Large Millimeter/submillimeter Array (ALMA); reaching an angular resolution of 25 µas, with characteristic sensitivity limits of $\sim 1 mJy$ on baselines to ALMA and $\sim 10 mJy$ on other baselines. The observations present challenges for existing data processing tools, arising from the rapid atmospheric phase fluctuations, wide recording bandwidth, and highly heterogeneous array. In response, we developed three independent pipelines for phase calibration and fringe detection, each tailored to the specific needs of the EHT. The final data products include calibrated total intensity amplitude and phase information. They are validated through a series of quality assurance tests that show consistency across pipelines and set limits on baseline systematic errors of 2 % in amplitude and 1° in phase. The M87 data reveal the presence of two nulls in correlated flux density at $\sim 3.4$ and $\sim 8.3 Głambda$ and temporal evolution in closure quantities, indicating intrinsic variability of compact structure on a timescale of days, or several light-crossing times for a few billion solar-mass black hole. These measurements provide the first opportunity to image horizon-scale structure in M87.

First M87 Event Horizon Telescope Results. IV. Imaging the Central Supermassive Black Hole

Mon, 01 Apr 2019 00:00:00 +0000

The Astrophysical Journal Letters, vol. 875, no. 1, pp. L4(52pp)

著者:

The Event Horizon Telescope Collaboration

URL:

DOI
arXiv

Abstract:

We present the first Event Horizon Telescope (EHT) images of M87, using observations from April 2017 at 1.3 mm wavelength. These images show a prominent ring with a diameter of $\sim 40 µas$, consistent with the size and shape of the lensed photon orbit encircling the ``shadow’’ of a supermassive black hole. The ring is persistent across four observing nights and shows enhanced brightness in the south. To assess the reliability of these results, we implemented a two-stage imaging procedure. In the first stage, four teams, each blind to the others’ work, produced images of M87 using both an established method (CLEAN) and a newer technique (regularized maximum likelihood). This stage allowed us to avoid shared human bias and to assess common features among independent reconstructions. In the second stage, we reconstructed synthetic data from a large survey of imaging parameters and then compared the results with the corresponding ground truth images. This stage allowed us to select parameters objectively to use when reconstructing images of M87. Across all tests in both stages, the ring diameter and asymmetry remained stable, insensitive to the choice of imaging technique. We describe the EHT imaging procedures, the primary image features in M87, and the dependence of these features on imaging assumptions.

First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring

Mon, 01 Apr 2019 00:00:00 +0000

The Astrophysical Journal Letters, vol. 875, no. 1, pp. L5(31pp)

著者:

The Event Horizon Telescope Collaboration

URL:

DOI
arXiv

Abstract:

The Event Horizon Telescope (EHT) has mapped the central compact radio source of the elliptical galaxy M87 at 1.3 mm with unprecedented angular resolution. Here we consider the physical implications of the asymmetric ring seen in the 2017 EHT data. To this end, we construct a large library of models based on general relativistic magnetohydrodynamic (GRMHD) simulations and synthetic images produced by general relativistic ray tracing. We compare the observed visibilities with this library and confirm that the asymmetric ring is consistent with earlier predictions of strong gravitational lensing of synchrotron emission from a hot plasma orbiting near the black hole event horizon. The ring radius and ring asymmetry depend on black hole mass and spin, respectively, and both are therefore expected to be stable when observed in future EHT campaigns. Overall, the observed image is consistent with expectations for the shadow of a spinning Kerr black hole as predicted by general relativity. If the black hole spin and M87’s large scale jet are aligned, then the black hole spin vector is pointed away from Earth. Models in our library of non-spinning black holes are inconsistent with the observations as they do not produce sufficiently powerful jets. At the same time, in those models that produce a sufficiently powerful jet, the latter is powered by extraction of black hole spin energy through mechanisms akin to the Blandford-Znajek process. We briefly consider alternatives to a black hole for the central compact object. Analysis of existing EHT polarization data and data taken simultaneously at other wavelengths will soon enable new tests of the GRMHD models, as will future EHT campaigns at 230 and 345 GHz.

First M87 Event Horizon Telescope Results. VI. The Shadow and Mass of the Central Black Hole

Mon, 01 Apr 2019 00:00:00 +0000

The Astrophysical Journal Letters, vol. 875, no. 1, pp. L6(44pp)

著者:

The Event Horizon Telescope Collaboration

URL:

DOI
arXiv

Abstract:

We present measurements of the properties of the central radio source in M87 using Event Horizon Telescope data obtained during the 2017 campaign. We develop and fit geometric crescent models (asymmetric rings with interior brightness depressions) using two independent sampling algorithms that consider distinct representations of the visibility data. We show that the crescent family of models is statistically preferred over other comparably complex geometric models that we explore. We calibrate the geometric model parameters using general relativistic magnetohydrodynamic (GRMHD) models of the emission region and estimate physical properties of the source. We further fit images generated from GRMHD models directly to the data. We compare the derived emission region and black hole parameters from these analyses with those recovered from reconstructed images. There is a remarkable consistency among all methods and data sets. We find that $>50 %$ of the total flux at arcsecond scales comes from near the horizon, and that the emission is dramatically suppressed interior to this region by a factor $>10$, providing direct evidence of the predicted shadow of a black hole. Across all methods, we measure a crescent diameter of $42 \pm 3 µas$ and constrain its fractional width to be $< 0.5$. Associating the crescent feature with the emission surrounding the black hole shadow, we infer an angular gravitational radius of $GM/Dc^2 = 3.8 \pm 0.4 µas$. Folding in a distance measurement of $16.8_-0.7^+0.8$ Mpc gives a black hole mass of $M=6.5\pm 0.2|_{\mathrmstat}\pm 0.7|_{\mathrmsys}\times 10^9$ $M_{\odot}$. This measurement from lensed emission near the event horizon is consistent with the presence of a central Kerr black hole, as predicted by the general theory of relativity.

SMILI: Sparse Modeling Imaging Library for Interferometry

Mon, 01 Apr 2019 00:00:00 +0000

Astrophysics Source Code Library

著者:

Kazunori Akiyama
Fumie Tazaki
Kotaro Moriyama
Ilje Cho
Shiro Ikeda
Mahito Sasada
Hiroki Okino
Mareki Honma

Abstract:

SMILI uses sparse sampling techniques and other regularization methods for interferometric imaging. The python-interfaced library is mainly designed for very long baseline interferometry, and has been under the active development primarily for the Event Horizon Telescope (EHT).

An image reconstruction method for X-ray telescope system with an angular resolution booster

Tue, 01 Jan 2019 00:00:00 +0000

Publications of the Astronomical Society of Japan, vol. 71, no. 1, pp. 24

著者:

Mikio Morii
Shiro Ikeda
Yoshitomo Maeda

URL:

DOI
arXiv

Abstract:

We propose an image reconstruction method for an X-ray telescope system with an angular resolution booster proposed by Maeda et al. (2018, PASJ, submitted). The system consists of double multi-grid masks in front of an X-ray mirror and an off-focused two-dimensional imager. Because the obtained image is off-focused, an additional image reconstruction process is assumed to be included. Our image reconstruction method is an extension of the traditional Richardson-Lucy algorithm with two regularization terms, one for sparseness and the other for smoothness. Such a combination is desirable for astronomical imaging because astronomical objects have a variety in shape, from point sources to diffuse sources to mixtures of both. The performance of the system is demonstrated with simulated data for point sources and diffuse X-ray sources such as Cas A and the Crab Nebula. The image resolution is improved from a few arcmin of focused image without the booster to a few arcsec with the booster. Through the demonstration, the angular resolution booster with the image reconstruction method is shown to be feasible.

Luminosity function of faint sporadic meteors measured with a wide-field CMOS mosaic camera Tomo-e PM

Tue, 01 Jan 2019 00:00:00 +0000

Planetary and Space Science, vol. 165, pp. 281–292

著者:

Ryou Ohsawa
Shigeyuki Sako
Yuki Sarugaku
Fumihiko Usui
Takafumi Ootsubo
Yasunori Fujiwara
Mikiya Sato
Toshihiro Kasuga
Ko Arimatsu
Jun-ichi Watanabe
Mamoru Doi
Naoto Kobayashi
Hidenori Takahashi
Kentaro Motohara
Tomoki Morokuma
Masahiro Konishi
Tsutomu Aoki
Takao Soyano
Ken’ichi Tarusawa
Yuki Mori
Yoshikazu Nakada
Makoto Ichiki
Noriaki Arima
Yuto Kojima
Masahiro Morita
Toshikazu Shigeyama
Yoshifusa Ita
Mitsuru Kokubo
Kazuma Mitsuda
Hiroyuki Maehara
Nozomu Tominaga
Takuya Yamashita
Shiro Ikeda
Mikio Morii
Seitaro Urakawa
Shin-ichiro Okumura
Makoto Yoshikawa

URL:

DOI
arXiv

Abstract:

Imaging observations of faint meteors were carried out on April 11 and 14, 2016 with a wide-field CMOS mosaic camera, Tomo-e PM, mounted on the 105-cm Schmidt telescope at Kiso Observatory, the University of Tokyo. Tomo-e PM, which is a prototype model of Tomo-e Gozen, can monitor a sky of $\sim$1.98$\sim$deg$^2$ at 2Hz. The numbers of detected meteors are 1514 and 706 on April 11 and 14, respectively. The detected meteors are attributed to sporadic meteors. Their absolute magnitudes range from $+4$ to $+10$mag in the V-band, corresponding to about $8.3\times10^-2$ to $3.3\times10^-4$g in mass. The present magnitude distributions we obtained are well explained by a single power-law luminosity function with a slope parameter $r=3.1\pm 0.4$ and a meteor rate $łog_10N0=-5.5\pm 0.5$. The results demonstrate a high performance of telescopic observations with a wide-field video camera to constrain the luminosity function of faint meteors. The performance of Tomo-e Gozenis about two times higher than that of Tomo-e PM. A survey with Tomo-e Gozenwill provide a more robust measurement of the luminosity function.

ブラックホールシャドウの撮影とスパースモデリング

Wed, 01 Aug 2018 00:00:00 +0000

数学セミナー, vol. 58, no. 8, pp. 41–45

著者:

池田思朗

キーワード:

天文データ科学
スパースモデリング
EHT

天文学におけるデータ科学的方法

Sun, 01 Jul 2018 00:00:00 +0000

パリティ, vol. 33, no. 8, pp. 16–17

著者:

池田思朗

キーワード:

天文データ科学

データ科学と天文学

Fri, 01 Jun 2018 00:00:00 +0000

天文月報, vol. 111, no. 7, pp. 460–467

著者:

池田思朗
森井幹雄

キーワード:

天文データ科学
スパースモデリング

URL:

Link

Abstract:

最近，機械学習や人工知能といったデータ科学分野の進展が目覚ましい．この20年ほど，応用数学分野の理論的進展と計算機の処理能力の飛躍的な向上が相まって，データ解析の手法が発展した結果である．こうした新たなデータ処理の方法は産業を通じた社会への貢献だけでなく，自然科学の分野にも影響を及ぼしていくはずである．実際に生物学をはじめ，すでに大きな変化をした分野が存在する．本稿では，天文学において人工知能や機械学習，統計学などのデータ科学分野の手法が今後どのような役割を担っていくのか考えていく．

Superresolution Interferometric Imaging with Sparse Modeling Using Total Squared Variation – Application to Imaging the Black Hole Shadow

Tue, 01 May 2018 00:00:00 +0000

The Astrophysical Journal, vol. 858, no. 1, pp. 56

著者:

Kazuki Kuramochi
Kazunori Akiyama
Shiro Ikeda
Fumie Tazaki
Vincent L. Fish
Hung-Yi Pu
Keiichi Asada
Mareki Honma

URL:

DOI
arXiv

Abstract:

We propose a new imaging technique for interferometry using sparse modeling, utilizing two regularization terms: the $\ell_1$-norm and a new function named total squared variation (TSV) of the brightness distribution. First, we demonstrate that our technique may achieve a superresolution of $\sim30 %$ compared with the traditional CLEAN beam size using synthetic observations of two point sources. Second, we present simulated observations of three physically motivated static models of Sgr A* with the Event Horizon Telescope (EHT) to show the performance of proposed techniques in greater detail. Remarkably, in both the image and gradient domains, the optimal beam size minimizing root-mean-squared errors is $łe 10$% of the traditional CLEAN beam size for $\ell_1+$ TSV regularization, and non-convolved reconstructed images have smaller errors than beam-convolved reconstructed images. This indicates that TSV is well matched to the expected physical properties of the astronomical images and the traditional post-processing technique of Gaussian convolution in interferometric imaging may not be required. We also propose a feature-extraction method to detect circular features from the image of a black hole shadow and use it to evaluate the performance of the image reconstruction. With this method and reconstructed images, the EHT can constrain the radius of the black hole shadow with an accuracy of $\sim10 %$ – 20 % in present simulations for Sgr A*, suggesting that the EHT would be able to provide useful independent measurements of the mass of the supermassive black holes in Sgr A* and also another primary target, M87.

``Slow-scanning'' in ground-based mid-infrared observations

Sun, 01 Apr 2018 00:00:00 +0000

The Astrophysical Journal, vol. 857, no. 1, pp. 37(11pp)

著者:

Ryou Ohsawa
Shigeyuki Sako
Takashi Miyata
Takafumi Kamizuka
Kazushi Okada
Kiyoshi Mori
Masahito S. Uchiyama
Junpei Yamaguchi
Takuya Fujiyoshi
Mikio Morii
Shiro Ikeda

URL:

DOI
arXiv

Abstract:

Chopping observations with a tip-tilt secondary mirror have conventionally been used in ground-based mid-infrared observations. However, it is not practical for next generation large telescopes to have a large tip-tilt mirror that moves at a frequency larger than a few hertz. We propose an alternative observing method, a slow-scanning'' observation. Images are continuously captured as movie data, while the field of view is slowly moved. The signal from an astronomical object is extracted from the movie data by a low-rank and sparse matrix decomposition. The performance of the slow-scanning’’ observation was tested in an experimental observation with Subaru/COMICS. The quality of a resultant image in the slow-scanning'' observation was as good as in a conventional chopping observation with COMICS, at least for a bright point-source object. The observational efficiency in the slow-scanning’’ observation was better than that in the chopping observation. The results suggest that the ``slow-scanning’’ observation can be a competitive method for the Subaru telescope and be of potential interest to other ground-based facilities to avoid chopping.

Exhaustive search for sparse variable selection in linear regression

Thu, 01 Mar 2018 00:00:00 +0000

Journal of the Physical Society of Japan, vol. 87, no. 4, pp. 044802

著者:

Yasuhiko Igarashi
Hikaru Takenaka
Yoshinori Nakanishi-Ohno
Makoto Uemura
Shiro Ikeda
Masato Okada

URL:

DOI
arXiv

Abstract:

We propose a K-sparse exhaustive search (ES-$K$) method and a $K$-sparse approximate exhaustive search method (AES-$K$) for selecting variables in linear regression. With these methods, K-sparse combinations of variables are tested exhaustively assuming that the optimal combination of explanatory variables is $K$-sparse. By collecting the results of exhaustively computing ES-$K$, various approximate methods for selecting sparse variables can be summarized as density of states. With this density of states, we can compare different methods for selecting sparse variables such as relaxation and sampling. For large problems where the combinatorial explosion of explanatory variables is crucial, the AES-$K$ method enables density of states to be effectively reconstructed by using the replica-exchange Monte Carlo method and the multiple histogram method. Applying the ES-$K$ and AES-$K$ methods to type Ia supernova data, we confirmed the conventional understanding in astronomy when an appropriate $K$ is given beforehand. However, we found the difficulty to determine $K$ from the data. Using virtual measurement and analysis, we argue that this is caused by data shortage.

Accelerating cross-validation with total variation and its application to super-resolution imaging

Fri, 01 Dec 2017 00:00:00 +0000

PLOS ONE, vol. 12, no. 12, pp. 1–14

著者:

Tomoyuki Obuchi
Shiro Ikeda
Kazunori Akiyama
Yoshiyuki Kabashima

URL:

DOI
arXiv

Abstract:

We develop an approximation formula for the cross-validation error (CVE) of a sparse linear regression penalized by $\ell_1$-norm and total variation terms, which is based on a perturbative expansion utilizing the largeness of both the data dimensionality and the model. The developed formula allows us to reduce the necessary computational cost of the CVE evaluation significantly. The practicality of the formula is tested through application to simulated black-hole image reconstruction on the event-horizon scale with super resolution. The results demonstrate that our approximation reproduces the CVE values obtained via literally conducted cross-validation with reasonably good precision.

Imaging the Schwarzschild-radius-scale Structure of M87 with the Event Horizon Telescope using Sparse Modeling

Wed, 01 Mar 2017 00:00:00 +0000

The Astrophysical Journal, vol. 838, no. 1, pp. 1(16pp)

著者:

Kazunori Akiyama
Kazuki Kuramochi
Shiro Ikeda
Vincent L. Fish
Fumie Tazaki
Mareki Honma
Sheperd S. Doeleman
Avery Broderick
Jason Dexter
Monika Mo'scibrodzka
Katherine L. Bouman
Andrew Chael
Masamichi Zaizen

URL:

DOI
arXiv

Abstract:

We propose a new imaging technique for radio and optical/infrared interferometry. The proposed technique reconstructs the image from the visibility amplitude and closure phase, which are standard data products of short-millimeter very long baseline interferometers such as the Event Horizon Telescope (EHT) and optical/infrared interferometers, by utilizing two regularization functions: the $\ell_1$-norm and total variation (TV) of the brightness distribution. In the proposed method, optimal regularization parameters, which represent the sparseness and effective spatial resolution of the image, are derived from data themselves using cross-validation (CV). As an application of this technique, we present simulated observations of M87 with the EHT based on four physically motivated models. We confirm that $\ell_1 +$ TV regularization can achieve an optimal resolution of $\sim 20$% – $30$ % of the diffraction limit $łambda$/$D_{\mathrmmax}$, which is the nominal spatial resolution of a radio interferometer. With the proposed technique, the EHT can robustly and reasonably achieve super-resolution sufficient to clearly resolve the black hole shadow. These results make it promising for the EHT to provide an unprecedented view of the event-horizon-scale structure in the vicinity of the supermassive black hole in M87 and also the Galactic center Sgr A*.

Superresolution Full-polarimetric Imaging for Radio Interferometry with Sparse Modeling

Wed, 01 Mar 2017 00:00:00 +0000

The Astronomical Journal, vol. 153, no. 4, pp. 159(12pp)

著者:

Kazunori Akiyama
Shiro Ikeda
Mollie Pleau
Vincent L. Fish
Fumie Tazaki
Kazuki Kuramochi
Avery E. Broderick
Jason Dexter
Monika Mo'scibrodzka
Michael Gowanlock
Mareki Honma
Sheperd S. Doeleman

URL:

DOI
arXiv

Abstract:

We propose a new technique for radio interferometry to obtain super-resolution full polarization images in all four Stokes parameters using sparse modeling. The proposed technique reconstructs the image in each Stokes parameter from the corresponding full-complex Stokes visibilities by utilizing two regularization functions: the $\ell_1$-norm and total variation (TV) of the brightness distribution. As an application of this technique, we present simulated linear polarization observations of two physically motivated models of M87 with the Event Horizon Telescope (EHT). We confirm that $\ell_1 + $TV regularization can achieve an optimal resolution of $\sim 25$–$30$% of the diffraction limit $łambda$/D$_{\mathrmmax}$, which is the nominal spatial resolution of a radio interferometer for both the total intensity (i.e. Stokes $I$) and linear polarizations (i.e. Stokes $Q$ and $U$). This optimal resolution is better than that obtained from the widely used Cotton-Schwab CLEAN algorithm or from using $\ell_1$ or TV regularizations alone. Furthermore, we find that $\ell_1 +$V regularization can achieve much better image fidelity in linear polarization than other techniques over a wide range of spatial scales, not only in the super-resolution regime, but also on scales larger than the diffraction limit. Our results clearly demonstrate that sparse reconstruction is a useful choice for high-fidelity full-polarimetric interferometric imaging.

Data Compression for the Tomo-e Gozen Using Low-rank Matrix Approximation

Sun, 01 Jan 2017 00:00:00 +0000

The Astrophysical Journal, vol. 835, no. 1, pp. 1(5pp)

著者:

Mikio Morii
Shiro Ikeda
Shigeyuki Sako
Ryou Ohsawa

URL:

DOI
arXiv

Abstract:

Optical wide-field surveys with a high cadence are expected to create a new field of astronomy, so-called ``movie astronomy,’’ in the near future. The amount of data from the observations will be huge, and hence efficient data compression will be indispensable. Here we propose a low-rank matrix approximation with sparse matrix decomposition as a promising solution to reduce the data size effectively while preserving sufficient scientific information. We apply one of the methods to the movie data obtained with the prototype model of the Tomo-e Gozen mounted on the 1.0 m Schmidt telescope of Kiso Observatory. Once full-scale observation with the Tomo-e Gozen commences, it will generate $\sim30 TB$ of data per night. We demonstrate that the data are compressed by a factor of about 10 in size without losing transient events like optical short transient point sources and meteors. The intensity of point sources can be recovered from the compressed data. The processing runs sufficiently fast, compared with the expected data-acquisition rate in the actual observing runs.

Data-driven approach to Type Ia supernovae: variable selection on the peak luminosity and clustering in visual analytics

Thu, 01 Dec 2016 00:00:00 +0000

Journal of Physics: Conference Series, vol. 699, pp. 012009(10pp)

著者:

Makoto Uemura
Koji S. Kawabata
Shiro Ikeda
Keiichi Maeda
Hsiang-Yun Wu
Kazuho Watanabe
Shigeo Takahashi
Issei Fujishiro

URL:

Abstract:

Type Ia supernovae (SNIa) have an almost uniform peak luminosity, so that they are used as ``standard candle’’ to estimate distances to galaxies in cosmology. In this article, we introduce our two recent works on SNIa based on data-driven approach. The diversity in the peak luminosity of SNIa can be reduced by corrections in several variables. The color and decay rate have been used as the explanatory variables of the peak luminosity in past studies. However, it is proposed that their spectral data could give a better model of the peak luminosity. We use cross-validation in order to control the generalization error and a LASSO-type estimator in order to choose the set of variables. Using 78 samples and 276 candidates of variables, we confirm that the peak luminosity depends on the color and decay rate. Our analysis does not support adding any other variables in order to have a better generalization error. On the other hand, this analysis is based on the assumption that SNIa originate in a single population, while it is not trivial. Indeed, several sub-types possibly having different nature have been proposed. We used a visual analytics tool for the asymmetric biclustering method to find both a good set of variables and samples at the same time. Using 14 variables and 132 samples, we found that SNIa can be divided into two categories by the expansion velocity of ejecta. Those examples demonstrate that the data-driven approach is useful for high-dimensional large-volume data which becomes common in modern astronomy.

Imaging black holes with sparse modeling

Thu, 01 Dec 2016 00:00:00 +0000

Journal of Physics: Conference Series, vol. 699, pp. 012006(9pp)

著者:

Mareki Honma
Kazunori Akiyama
Fumie Tazaki
Kazuki Kuramochi
Shiro Ikeda
Kazuhiro Hada
Makoto Uemura

URL:

Abstract:

We introduce a new imaging method for radio interferometry based on sparse- modeling. The direct observables in radio interferometry are visibilities, which are Fourier transformation of an astronomical image on the sky-plane, and incomplete sampling of visibilities in the spatial frequency domain results in an under-determined problem, which has been usually solved with 0 filling to un-sampled grids. In this paper we propose to directly solve this under-determined problem using sparse modeling without 0 filling, which realizes super resolution, i.e., resolution higher than the standard refraction limit. We show simulation results of sparse modeling for the Event Horizon Telescope (EHT) observations of super-massive black holes and demonstrate that our approach has significant merit in observations of black hole shadows expected to be realized in near future. We also present some results with the method applied to real data, and also discuss more advanced techniques for practical observations such as imaging with closure phase as well as treating the effect of interstellar scattering effect.

Improved in-cell structure determination of proteins at near-physiological concentration

Thu, 01 Dec 2016 00:00:00 +0000

Scientific Reports, vol. 6, pp. 38312(11pp)

著者:

Teppei Ikeya
Tomomi Hanashima
Saori Hosoya
Manato Shimazaki
Shiro Ikeda
Masaki Mishima
Peter Güntert
Yutaka Ito

URL:

Abstract:

Investigating three-dimensional (3D) structures of proteins in living cells by in-cell nuclear magnetic resonance (NMR) spectroscopy opens an avenue towards understanding the structural basis of their functions and physical properties under physiological conditions inside cells. In-cell NMR provides data at atomic resolution non-invasively, and has been used to detect protein-protein interactions, thermodynamics of protein stability, the behavior of intrinsically disordered proteins, etc. in cells. However, so far only a single \itshape de novo 3D protein structure could be determined based on data derived only from in-cell NMR. Here we introduce methods that enable in-cell NMR protein structure determination for a larger number of proteins at concentrations that approach physiological ones. The new methods comprise (1) advances in the processing of non-uniformly sampled NMR data, which reduces the measurement time for the intrinsically short-lived in-cell NMR samples, (2) automatic chemical shift assignment for obtaining an optimal resonance assignment, and (3) structure refinement with Bayesian inference, which makes it possible to calculate accurate 3D protein structures from sparse data sets of conformational restraints. As an example application we determined the structure of the B1 domain of protein G at about 250 µM concentration in living \itshape E. coli cells.

Protein NMR Structure Refinement based on Bayesian Inference

Thu, 01 Dec 2016 00:00:00 +0000

Journal of Physics: Conference Series, vol. 699, pp. 012005(14pp)

著者:

Teppei Ikeya
Shiro Ikeda
Takanori Kigawa
Yutaka Ito
Peter Güntert

URL:

Abstract:

Nuclear Magnetic Resonance (NMR) spectroscopy is a tool to investigate threedimensional (3D) structures and dynamics of biomacromolecules at atomic resolution in solution or more natural environments such as living cells. Since NMR data are principally only spectra with peak signals, it is required to properly deduce structural information from the sparse experimental data with their imperfections and uncertainty, and to visualize 3D conformations by NMR structure calculation. In order to efficiently analyse the data, Rieping et al. proposed a new structure calculation method based on Bayes’ theorem. We implemented a similar approach into the program CYANA with some modifications. It allows us to handle automatic NOE cross peak assignments in unambiguous and ambiguous usages, and to create a prior distribution based on a physical force field with the generalized Born implicit water model. The sampling scheme for obtaining the posterior is performed by a hybrid Monte Carlo algorithm combined with Markov chain Monte Carlo (MCMC) by the Gibbs sampler, and molecular dynamics simulation (MD) for obtaining a canonical ensemble of conformations. Since it is not trivial to search the entire function space particularly for exploring the conformational prior due to the extraordinarily large conformation space of proteins, the replica exchange method is performed, in which several MCMC calculations with different temperatures run in parallel as replicas. It is shown with simulated data or randomly deleted experimental peaks that the new structure calculation method can provide accurate structures even with less peaks, especially compared with the conventional method. In particular, it dramatically improves in-cell structures of the proteins GB1 and TTHA1718 using exclusively information obtained in living \itshape Escherichia coli (\itshape E. coli) cells.

Sparse Modeling for Astronomical Data Analysis

Thu, 01 Dec 2016 00:00:00 +0000

Journal of Physics: Conference Series, vol. 699, pp. 012008(4pp)

著者:

Shiro Ikeda
Hirokazu Odaka
Makoto Uemura

URL:

Abstract:

For astronomical data analysis, there have been proposed multiple methods based on sparse modeling. We have proposed a method for Compton camera imaging. The proposed approach is a sparse modeling method, but the derived algorithm is different from LASSO. We explain the problem and how we derived the method.

Machine-learning Selection of Optical Transients in Subaru/Hyper Suprime-Cam Survey

Sat, 01 Oct 2016 00:00:00 +0000

Publications of the Astronomical Society of Japan, vol. 68, no. 6, pp. 104(8pp)

著者:

Mikio Morii
Shiro Ikeda
Nozomu Tominaga
Masaomi Tanaka
Tomoki Morokuma
Katsuhiko Ishiguro
Junji Yamato
Naonori Ueda
Naotaka Suzuki
Naoki Yasuda
Naoki Yoshida

URL:

DOI
arXiv

Abstract:

We present an application of machine-learning (ML) techniques to source selection in the optical transient survey data with the Hyper Suprime-Cam (HSC) on the Subaru telescope. Our goal is to select real transient events accurately and in a timely manner out of a large number of false candidates, obtained by the standard difference-imaging method. We have developed the transient selector, which is based on majority voting of the three ML machines of AUC Boosting, Random Forest, and Deep Neural Networks. We applied it to our observing runs of Subaru-HSC in 2015 May and August, and proved it to be efficient in selecting optical transients. The false positive rate was 1.0% at the true positive rate of 90 % in the magnitude range of 22.0–25.0 mag for the May data. For the August run, we successfully detected and reported 10 supernovae candidates within the same day as the observation. From these runs, we learned the following lessons: (1) training using artificial objects is effective in filtering false candidates out, especially for faint objects, and (2) a combination of ML by majority voting is advantageous.

Rate-Distortion Functions for Gamma-type Sources under Absolute-log Distortion Measure

Sat, 01 Oct 2016 00:00:00 +0000

IEEE Transactions on Information Theory, vol. 62, no. 10, pp. 5496–5502

著者:

Kazuho Watanabe
Shiro Ikeda

URL:

Abstract:

When the information source is a continuous distribution and the rate-distortion function is strictly larger than the Shannon lower bound, the explicit evaluation of the rate-distortion function is not straightforward. We evaluate the rate-distortion function for an independent identically distributed gamma source with respect to the absolute-log distortion measure. The logarithmic transformation reduces this rate-distortion problem to that under the absolute distortion measure. Extending the explicit evaluation of the rate-distortion function for the Gaussian sources, we obtain the parametric form of the rate-distortion function. We show that the optimal distribution of reconstruction consists of a continuous component enclosed by left and right discrete components, and the left discrete component vanishes when the acceptable distortion is small. We further extend the result for a wider class of source distributions.

PRECL: A new method for interferometry imaging from closure phase

Fri, 01 Apr 2016 00:00:00 +0000

Publications of the Astronomical Society of Japan, vol. 68, no. 3, pp. 45(9pp)

著者:

Shiro Ikeda
Fumie Tazaki
Kazunori Akiyama
Kazuhiro Hada
Mareki Honma

URL:

DOI
arXiv

Abstract:

For short-wavelength VLBI observations, it is difficult to measure the phase of the visibility function accurately. The closure phases are reliable measurements under this situation, though it is not sufficient to retrieve all of the phase information. We propose a new method, phase retrieval from closure phase (PRECL). PRECL estimates all the visibility phases only from the closure phases. Combining PRECL with a sparse modeling method we have already proposed, the imaging process of VLBI does not rely on a dirty image or self-calibration. The proposed method is tested numerically and the results are promising.

Risk assessment of radioisotope contamination for aquatic living resources in and around Japan

Mon, 01 Feb 2016 00:00:00 +0000

Proceedings of the National Academy of Sciences (PNAS), vol. 113, no. 14, pp. 3838–3843

著者:

Hiroshi Okamura
Shiro Ikeda
Takami Morita
Shinto Eguchi

URL:

Abstract:

Quantification of contamination risk caused by radioisotopes released from the Fukushima Dai-ichi nuclear power plant is useful for excluding or reducing groundless rumors about food safety. Our new statistical approach made it possible to evaluate the risk for aquatic food and showed that the present contamination levels of radiocesiums are low overall. However, some freshwater species still have relatively high risks. We also suggest the necessity of refining data collection plans to reduce detection limits in the future, because a small number of precise measurements are more valuable than many measurements that are below detection limits.

An asymmetric logistic regression model for ecological data

Thu, 01 Oct 2015 00:00:00 +0000

Methods in Ecology and Evolution, vol. 7, no. 2, pp. 249–260

著者:

Osamu Komori
Shinto Eguchi
Shiro Ikeda
Hiroshi Okamura
Momoko Ichinokawa
Shinichiro Nakayama

URL:

Abstract:

Binary data are popular in ecological and environmental studies; however, due to various uncertainties and complexities present in data sets, the standard generalized linear model with a binomial error distribution often demonstrates insufficient predictive performance when analysing binary and proportional data. 2. To address this difficulty, we propose an asymmetric logistic regression model that uses a new parameter to account for data complexity. We observe that this parameter controls the model’s asymmetry and is important for adjusting the weights associated with observed data in order to improve model fitting. This model includes the ordinary logistic regression model as a special case. It is easily implemented using a slight modification of glm or glmer in statistical software R. 3. Simulation studies suggest that our new approach outperforms a traditional approach in terms of both predictive accuracy and variable selection. In a case study involving fisheries data, we found that the annual catch amount had a greater impact on stock status prediction, and improved predictive capability was supported with a smaller AIC compared to a generalized linear model. 4. In summary, our method can enhance the applicability of a generalized linear model to various ecological problems using a slight modification, and significantly improves model fitting and model selection.

Variable Selection for Modeling the Absolute Magnitude at Maximum of Type Ia Supernovae

Mon, 01 Jun 2015 00:00:00 +0000

Publications of the Astronomical Society of Japan, vol. 67, no. 3, pp. 55(9pp)

著者:

Makoto Uemura
Koji S. Kawabata
Shiro Ikeda
Keiichi Maeda

URL:

DOI
arXiv

Abstract:

We discuss what is an appropriate set of explanatory variables in order to predict the absolute magnitude at the maximum of Type Ia supernovae. In order to have a good prediction, the error for future data, which is called the ``generalization error,’’ should be small. We use cross-validation in order to control the generalization error and a LASSO-type estimator in order to choose the set of variables. This approach can be used even in the case that the number of samples is smaller than the number of candidate variables. We studied the Berkeley supernova database with our approach. Candidates for the explanatory variables include normalized spectral data, variables about lines, and previously proposed flux ratios, as well as the color and light-curve widths. As a result, we confirmed the past understanding about Type Ia supernovae: (i) The absolute magnitude at maximum depends on the color and light-curve width. (ii) The light-curve width depends on the strength of Si - II. Recent studies have suggested adding more variables in order to explain the absolute magnitude. However, our analysis does not support adding any other variables in order to have a better generalization error.

Entropic Risk Minimization for Nonparametric Estimation of Mixing Distributions

Wed, 01 Apr 2015 00:00:00 +0000

Machine Learning, vol. 99, no. 1, pp. 119–136

著者:

Kazuho Watanabe
Shiro Ikeda

URL:

Abstract:

We discuss a nonparametric estimation method for the mixing distributions in mixture models. The problem is formalized as a minimization of a one-parameter objective functional, which becomes the maximum likelihood estimation or the kernel vector quantization in special cases. Generalizing the theorem for the nonparametric maximum likelihood estimation, we prove the existence and discreteness of the optimal mixing distribution and provide an algorithm to calculate it. It is demonstrated that with an appropriate choice of the parameter, the proposed method is less prone to overfitting than the maximum likelihood method. We further discuss the connection between the unifying estimation framework and the rate-distortion problem.

スパースモデリングと天文学

Sun, 01 Mar 2015 00:00:00 +0000

応用数理, vol. 25, no. 1, pp. 15–19

著者:

池田思朗
本間希樹
植村誠

キーワード:

スパースモデリング
天文データ科学

URL:

Bin mode estimation methods for Compton camera imaging

Wed, 01 Oct 2014 00:00:00 +0000

Nuclear Instruments and Methods in Physics Research A, vol. 760, pp. 46–56

著者:

Shiro Ikeda
Hirokazu Odaka
Makoto Uemura
Tadayuki Takahashi
Shin Watanabe
Shin’ichiro Takeda

URL:

DOI
arXiv

Abstract:

We study the image reconstruction problem of a Compton camera which consists of semiconductor detectors. The image reconstruction is formulated as a statistical estimation problem. We employ a bin-mode estimation (BME) and extend an existing framework to a Compton camera with multiple scatterers and absorbers. Two estimation algorithms are proposed: an accelerated EM algorithm for the maximum likelihood estimation (MLE) and a modified EM algorithm for the maximum a posteriori (MAP) estimation. Numerical simulations demonstrate the potential of the proposed methods.

Super-resolution imaging with radio interferometry using sparse modeling

Wed, 01 Oct 2014 00:00:00 +0000

Publications of the Astronomical Society of Japan, vol. 66, no. 5, pp. 95(14pp)

著者:

Mareki Honma
Kazunori Akiyama
Makoto Uemura
Shiro Ikeda

URL:

DOI
arXiv

Abstract:

We propose a new technique to obtain super-resolution images with radio interferometry using sparse modeling. In standard radio interferometry, sampling of $(u,v)$ is quite often incomplete and thus obtaining an image from observed visibilities becomes an underdetermined problem, and a technique of so-called ``zero-padding’’ is often used to fill up unsampled grids in the $(u,v)$ plane, resulting in image degradation by finite beam size as well as numerous side-lobes. In this paper we show that directly solving such an underdetermined problem based on sparse modeling (in this paper, Least Absolute Shrinkage and Selection Operator, known as LASSO) avoids the above problems introduced by zero-padding, leading to super-resolution images in which structure finer than the standard beam size (diffraction limit) can be reproduced. We present results of one-dimensional and two-dimensional simulations of interferometric imaging, and discuss its implications for super-resolution imaging, particularly focusing on imaging of black hole shadows with millimeter VLBI (Very Long Baseline Interferometry).

Introduction to the issue on differential geometry in signal processing

Thu, 01 Aug 2013 00:00:00 +0000

IEEE Journal of Selected Topics in Signal Processing, vol. 7, no. 4, pp. 573–575

著者:

Jonathan H. Manton
David Applebaum
Shiro Ikeda
Nicolas LeBihan

URL:

X線自由電子レーザーによる分子の電子密度推定

Tue, 01 Jan 2013 00:00:00 +0000

統計数理, vol. 61, no. 1, pp. 135–146

著者:

池田思朗
河野秀俊

キーワード:

スパースモデリング
X線回折
単粒子構造解析

URL:

Link

Abstract:

米国，欧州，日本及び韓国ではX線自由電子レーザーと呼ばれる装置が開発され，米国，日本では運用段階にある．現在，この装置によって初めて可能となったX線領域の波長を持つ高強度レーザー光を用いた，様々な実験が計画および実施されている．本稿では，そうした実験のひとつ，X線回折を用いた生体単粒子の電子密度推定について説明し，2次元回折画像から2次元電子密度を推定する位相回復問題に対する我々の研究成果について解説する．

弱い回析パターンからの位相回復単粒子構造解析に向けて

Tue, 01 Jan 2013 00:00:00 +0000

放射光, vol. 26, no. 1, pp. 38–43

著者:

河野秀俊
池田思朗

キーワード:

スパースモデリング
X線回折
単粒子構造解析

URL:

Link

Abstract:

SPring8に建設された短パルスかつ大強度のコヒーレントX線源は、生体高分子など単粒子での構造解析が期待されている。しかし、この従来の10億倍の輝度を持つ光を照射すると粒子は破壊されてしまうため、そうなる前の短時間(数fs以内)に回折パターンを観測しなくてはならない。そのため、測定される回折強度は弱いものになってしまう。われわれは、従来の方法よりも粗い回折パターンから位相回復できるベイズ統計にもとづいたアルゴリズムを開発したので、本稿で紹介する。

Phase retrieval from single biomolecule diffraction pattern

Wed, 01 Feb 2012 00:00:00 +0000

Optics Express, vol. 20, no. 4, pp. 3375–3387

著者:

Shiro Ikeda
Hidetoshi Kono

URL:

DOI
arXiv

Abstract:

In this paper, we propose the SPR (sparse phase retrieval) method, which is a new phase retrieval method for coherent x-ray diffraction imaging (CXDI). Conventional phase retrieval methods effectively solve the problem for high signal-to-noise ratio measurements, but would not be sufficient for single biomolecular imaging which is expected to be realized with femto-second x-ray free electron laser pulses. The SPR method is based on the Bayesian statistics. It does not need to set the object boundary constraint that is required by the commonly used hybrid input-output (HIO) method, instead a prior distribution is defined with an exponential distribution and used for the estimation. Simulation results demonstrate that the proposed method reconstructs the electron density under a noisy condition even some central pixels are masked.

通信路容量と確率測度の最適化–最適な変調方式のために–

Sun, 01 Jan 2012 00:00:00 +0000

電子情報通信学会基礎・境界ソサイエティ Fundamentals Review, vol. 5, no. 3, pp. 230–238

著者:

池田思朗

キーワード:

通信路容量，最大出力制約，変調方式
無限次元最適化

URL:

Abstract:

通信路容量は，情報理論，通信理論において重要な役割を持つ量である．また，その通信路容量を達成する入力の確率分布は最適な変調方式を与えるため，実用上も重要である．本稿では，連続値を入出力とする通信路について，通信路容量とそれを達成する入力の分布について考察する．入力が連続値を取り得る場合，一見すると連続な測度を持つ分布が最適となりそうだが，実際には多くの通信路と入力の制約のもとで，離散値のみを取る離散測度が通信路容量を達成する入力の分布となることが知られている.このような研究は1970年代に始まり様々な通信路に対する考察がなされてきたが，国内ではほとんど研究されていない．本稿では既知の事実を証明の概要とともに示し，通信工学への応用について考える．

An Introductory Review of Information Theory in the Context of Computational Neuroscience

Fri, 01 Jul 2011 00:00:00 +0000

Biological Cybernetics, vol. 105, no. 1, pp. 55–70

著者:

Mark D. McDonnell
Shiro Ikeda
Jonathan H. Manton

URL:

DOI
arXiv

Abstract:

This article introduces several fundamental concepts in information theory from the perspective of their origins in engineering. Understanding such concepts is important in neuroscience for two reasons. Simply applying formulae from information theory without understanding the assumptions behind their definitions can lead to erroneous results and conclusions. Furthermore, this century will see a convergence of information theory and neuroscience; information theory will expand its foundations to incorporate more comprehensively biological processes thereby helping reveal how neuronal networks achieve their remarkable information processing abilities.

2クラス判別器の組み合せによる多クラス判別統計モデルとパラメータ推定

Wed, 01 Dec 2010 00:00:00 +0000

統計数理, vol. 58, no. 2, pp. 157-166

著者:

池田思朗

キーワード:

Bradley-Terry モデル
多クラス判別

URL:

Link

Abstract:

機械学習の分野では，2クラス判別器を組み合わせて多クラスの判別器を作る様々な試みがなされている．Error Correcting Output Codes (ECOC) と呼ばれる方法が頻繁に用いれているが，それぞれの2クラス判別器が軟判定を返す場合にはECOCの他にもBradley-Terry (BT)モデルを用いる方法が提案されている．本稿ではこのBTモデルを用いる組み合わせ法を統計モデルとして考え，既存の方法の改善法のひとつを示す．

Combining binary machines for multi-class: Statistical model and parameter estimation

Mon, 01 Mar 2010 00:00:00 +0000

Journal of Physics: Conference Series, vol. 233, pp. 012006

著者:

Shiro Ikeda

URL:

Abstract:

Combining binary machines for multi-class classification problems is a popular idea, and many related methods have been proposed. When each binary machine reports a hard decision (a binary classifier), one of the most popular methods is to use the error correcting output codes (ECOC), while when each machine reports a soft decision (a binary predictor), another interesting idea is to use the Bradley-Terry (BT) model. In this paper, these methods are reviewed from a statistical viewpoint. As a result, a common framework will be given and natural extensions are derived for both of the ECOC and the BT model approaches.

Capacity of a single spiking neuron

Tue, 01 Sep 2009 00:00:00 +0000

Journal of Physics: Conference Series, International Workshop on Statistical-Mechanical Informatics 2009 (IW-SMI2009), vol. 197, pp. 012014

著者:

Shiro Ikeda
Jonathan H. Manton

URL:

Abstract:

It is widely believed the neurons transmit information in the form of spikes. Since the spike patterns are known to be noisy, the neuron information channel is noisy. We have investigated the channel capacity of this Spiking neuron channel'' for both of the temporal coding’’ and the ``rate coding,’’ which are two main coding considered in the neuroscience. As the result, we’ve proved that the distribution of inputs, which achieves the channel capacity, is a discrete distribution with finite mass points for temporal and rate coding under a reasonable assumption. In this draft, we show the details of the proof.

Capacity of a Single Spiking Neuron Channel

Mon, 01 Jun 2009 00:00:00 +0000

Neural Computation, vol. 21, no. 6, pp. 1714–1748

著者:

Shiro Ikeda
Jonathan H. Manton

URL:

Abstract:

Information transfer through a single neuron is a fundamental component of information processing in the brain, and computing the information channel capacity is important to understand this information processing. The problem is difficult since the capacity depends on coding, characteristics of the communication channel, and optimization over input distributions, among other issues. In this letter, we consider two models. The temporal coding model of a neuron as a communication channel assumes the output is tau where tau is a gamma-distributed random variable corresponding to the interspike interval, that is, the time it takes for the neuron to fire once. The rate coding model is similar; the output is the actual rate of firing over a fixed period of time. Theoretical studies prove that the distribution of inputs, which achieves channel capacity, is a discrete distribution with finite mass points for temporal and rate coding under a reasonable assumption. This allows us to compute numerically the capacity of a neuron. Numerical results are in a plausible range based on biological evidence to date.

Channel Estimation and Code Word Inference for Mobile Digital Satellite Broadcasting Reception

Mon, 01 Dec 2008 00:00:00 +0000

IEICE trans. on Communications, vol. E91-B, no. 12, pp. 3886–3898

著者:

Masatoshi Hamada
Shiro Ikeda

URL:

Abstract:

This paper proposes a method of improving reception of digital satellite broadcasting in a moving vehicle. According to some studies, the antennas used for mobile reception will be smaller in the next generation and reception will be more difficult because of a fading multipath channel with delays in a low carrier-to-noise ratio. Commonly used approaches to reduce the inter symbol interference caused by a fading multipath channel with delays are pilot sequences and diversity reception. Digital satellite broadcasting, however, does not transmit pilot sequences for channel estimation and it is not possible to install multiple antennas in a vehicle. This paper does not propose any change to the broadcasting standards but discusses how to process currently available digital satellite signals to obtain better results. Our method does not rely on the pilot sequences or diversity reception, but consists of channel estimation and stochastic inference methods. For each task, two methods are proposed. The maximum likelihood estimation and higher order statistics matching methods are proposed for the estimation, and the marginal with the joint probability inference methods are proposed for the stochastic inference. The improvements were confirmed through experiments with numerical simulations and real data. The computational costs are also discussed for future implementation.

通信路推定と誤り訂正による衛星デジタル放送移動受信の改善

Mon, 01 Dec 2008 00:00:00 +0000

統計数理, vol. 56, no. 2, pp. 215–224

著者:

浜田正稔
池田思朗

キーワード:

通信路モデル
確率推論

URL:

Link

Abstract:

本論文では，衛星デジタル放送の移動体における受信の問題を扱う．現在，衛星デジタル放送では移動体においては固定局と同様なシステムでは満足な受信はできない．この問題に対して，通信路の確率モデルを考え，その推定を行ない，確率モデルに基づく推論を行なうことで受信品質の改善を目指す．本稿で提案する通信路モデルは重回帰モデルである．パラメータ推定に対しては，二つの方法を提案する．放送受信では実時間処理が重要であることから，本提案手法は実時間で処理できる簡便なものである．提案する手法は実際に自動車を走行させて計測したデータによって実験を行ない，どの程度の受信品質の改善が得られるのか検証を行なった．

Motor Planning and Sparse Motor Command Representation

Fri, 01 Jun 2007 00:00:00 +0000

Neurocomputing, vol. 70, no. Issues 10-12, pp. 1748–1752

著者:

Yutaka Sakaguchi
Shiro Ikeda

URL:

Abstract:

The present article proposes a novel computational approach to the motor planning. In this approach, each motor command is represented as a linear combination of prefixed basis patterns, and the command for a given task is designed by minimizing a two-termed criterion consisting of a task optimization term and a parameter preference (i.e., sparseness) term. The result of a computer simulation with a single-joint reaching task confirmed that our ``representation-based’’ criterion for motor planning appropriately worked, together with showing that the resultant trajectory qualitatively replicated Fitts’ law.

確率的情報処理としての移動体通信(2) ターボ復号法の情報幾何的理解と改善の可能性

Thu, 01 Dec 2005 00:00:00 +0000

数理科学, no. 500, pp. 63–69

著者:

池田思朗

キーワード:

確率伝搬法
情報幾何
ターボ符号

Information Geometry for Turbo Decoding

Sat, 01 Jan 2005 00:00:00 +0000

Systems and Computers in Japan, vol. 36, no. 1, pp. 79–87

著者:

Shiro Ikeda
Toshiyuki Tanaka
Shun-ichi Amari

URL:

Abstract:

Turbo codes are known as a class of error-correcting codes which have high error-correcting performance with efficient decoding algorithm. Characteristics of the iterative decoding algorithm have been studied in detail through a variety of numerical experiments, but theoretical results are still insufficient. In this paper, this issue is addressed from the information geometrical viewpoint. As a result, a mathematical framework for analyzing turbo codes is obtained, and some of the fundamental properties of turbo decoding are elucidated based on this framework. Recently, it has been pointed out that the turbo decoding algorithm is related to the decoding algorithm of low-density parity check codes, the computation method of Bethe approximation in statistical physics, and the belief propagation algorithm of Bayesian networks. The mathematical framework given in the present paper can also be used to analyze these wide classes of iterative computation methods, and hence represent a new analysis tool.

情報幾何学に基づく確率伝搬法の解析

Wed, 01 Dec 2004 00:00:00 +0000

統計数理, vol. 52, no. 2, pp. 393–405

著者:

池田思朗
田中利幸
甘利俊一

キーワード:

確率伝搬法
情報幾何
グラフィカルモデル

URL:

Link

Abstract:

1980年代後半Pearlが提案した確率伝搬法は，大規模なグラフィカルモデルに対する確率推論のための計算手法である．同等の手法は統計物理学，統計学，誤り訂正符号の復号法などにも存在し，広く用いられている．確率伝搬法は木の構造のグラフに対してはグラフの大きさに比例した計算量で厳密解が得られる．しかしループを持つグラフに対しては繰り返し計算の収束性，および得られた結果の近似精度ともに理論的には十分理解されていなかった．一方で確率伝搬法は実用上有効な手法であり，その性質を理論的に明らかにすることは重要である．本研究では情報幾何学に基づく枠組みにより確率伝搬法を表現し，収束性や近似精度を議論する．

Stochastic Reasoning, Free Energy, and Information Geometry

Wed, 01 Sep 2004 00:00:00 +0000

Neural Computation, vol. 16, no. 9, pp. 1779–1810

著者:

Shiro Ikeda
Toshiyuki Tanaka
Shun-ichi Amari

URL:

Abstract:

Belief propagation is a universal method of stochastic reasoning. It gives a good approximate solution, when it is applied to a stochastic model with loopy interactions. AI, statistical physical, and information geometrical methods have so far been used to analyze its performance separately. The present paper gives a unified framework to understand the relation underlying these concepts. In particular, the free energy and its relation to BP and CCCP is elucidated from the point of view of information geometry. We then propose a family of new algorithms. The stability of the algorithms is also analyzed, and methods of accelerating these algorithms are proposed.

確率伝搬法の情報幾何–符号理論，統計物理，人工知能の接点–

Wed, 01 Sep 2004 00:00:00 +0000

応用数理, vol. 14, no. 3, pp. 24–35

著者:

池田思朗
田中利幸
甘利俊一

キーワード:

確率伝搬法
情報幾何
グラフィカルモデル
ターボ符号

URL:

Information geometry of turbo and low-density parity-check codes

Tue, 01 Jun 2004 00:00:00 +0000

IEEE Transactions on Information Theory, vol. 50, no. 6, pp. 1097–1114

著者:

Shiro Ikeda
Toshiyuki Tanaka
Shun-ichi Amari

URL:

Abstract:

Since the proposal of turbo codes in 1993, many studies have appeared on this simple and new type of codes which give a powerful and practical performance of error correction. Although experimental results strongly support the efficacy of turbo codes, further theoretical analysis is necessary, which is not straightforward. It is pointed out that the iterative decoding algorithm of turbo codes shares essentially similar ideas with low-density parity-check (LDPC) codes, with Pearl’s belief propagation algorithm applied to a cyclic belief diagram, and with the Bethe approximation in statistical physics. Therefore, the analysis of the turbo decoding algorithm will reveal the mystery of those similar iterative methods. In this paper, we recapture and extend the geometrical framework initiated by Richardson to the information geometrical framework of dual affine connections, focusing on both of the turbo and LDPC decoding algorithms. The framework helps our intuitive understanding of the algorithms and opens a new prospect of further analysis. We reveal some properties of these codes in the proposed framework, including the stability and error analysis. Based on the error analysis, we finally propose a correction term for improving the approximation.

Combined Approach of Array Processing and Independent Component Analysis for Blind Separation of Acoustic Signals

Thu, 01 May 2003 00:00:00 +0000

IEEE transactions on Audio and Speech Processing, vol. 11, no. 3, pp. 204–215

著者:

Futoshi Asano
Shiro Ikeda
Michiaki Ogawa
Hideki Asoh
Nobuhiko Kitawaki

URL:

Abstract:

In this paper, two array signal processing techniques are combined with independent component analysis (ICA) to enhance the performance of blind separation of acoustic signals in a reflective environment. The first technique is the subspace method which reduces the effect of room reflection when the system is used in a room. Room reflection is one of the biggest problems in blind source separation (BSS) in acoustic environments. The second technique is a method of solving permutation. For employing the subspace method, ICA must be used in the frequency domain, and precise permutation is necessary for all frequencies. In this method, a physical property of the mixing matrix, i.e., the coherency in adjacent frequencies, is utilized to solve the permutation. The experiments in a meeting room showed that the subspace method improved the rate of automatic speech recognition from 50% to 68% and that the method of solving permutation achieves performance that closely approaches that of the correct permutation, differing by only 4% in recognition rate.

独立成分解析

Sun, 01 Sep 2002 00:00:00 +0000

日本神経回路学会誌, vol. 9, no. 2, pp. 181–189

著者:

池田思朗

キーワード:

独立成分分析

URL:

両耳処理と独立成分解析

Mon, 01 Jul 2002 00:00:00 +0000

日本音響学会誌, vol. 58, no. 3, pp. 199–204

著者:

池田思朗

キーワード:

独立成分分析

URL:

ターボ復号の情報幾何

Wed, 01 May 2002 00:00:00 +0000

電子情報通信学会論文誌, vol. J85-D-II, no. 5, pp. 758–765

著者:

池田思朗
田中利幸
甘利俊一

キーワード:

ターボ符号
情報幾何

URL:

Link

Abstract:

ターボ符号は高い誤り訂正能力をもち，かつ効率の良い復号法をもつ誤り訂正符号として知られている．繰返しアルゴリズムを用いる復号法の特性については，様々な数値実験を通じて細かく調べられ，有効性が示されているが，理論的な結果は十分には得られていない．本論文では情報幾何学的観点からこの問題を扱う．その結果，ターボ符号を解析するための数学的枠組みを与え，その枠組みのもとでターボ復号解のもついくつかの基本的性質を明らかにする．本論文ではターボ符号に対する情報幾何を特に扱うが，近年，ターボ復号アルゴリズムが低密度パリティ検査符号の復号アルゴリズム，また統計物理におけるBethe近似の計算法，更にはベイジアンネットワークの確率伝搬アルゴリズムと対応づけられることが指摘されている．本研究の結果はこれらの広いクラスの反復計算手法に対しても有効であり，したがって新たな解析手法となる．

An Approach to Blind Source Separation Based on Temporal Structure of Speech Signals

Mon, 01 Oct 2001 00:00:00 +0000

Neurocomputing, vol. 41, no. 1-4, pp. 1–24

著者:

Noboru Murata
Shiro Ikeda
Andreas Ziehe

URL:

Abstract:

In this paper we introduce a new technique for blind source separation of speech signals. We focus on the temporal structure of the signals in contrast to most other major approaches to this problem. The idea is to apply the decorrelation method proposed by Molgedey and Schuster in the time-frequency domain. We show some results of experiments with both artificially controlled data and speech data recorded in the real environment.

Independent Component Analysis for Noisy Data –MEG data analysis

Fri, 01 Dec 2000 00:00:00 +0000

Neural Networks, vol. 13, no. 10, pp. 1063–1074

著者:

Shiro Ikeda
Keisuke Toyama

URL:

Abstract:

Information geometry is applied to mean field approximation for elucidating its properties in the spin glass model or the Boltzmann machine. The $\alpha$-divergence is used for approximation, where $\alpha$-geodesic projection plays an important role. The naive mean field approximation and TAP approximation are studied from the point of view of information geometry, which treats the intrinsic geometric structures of a family of probability distributions. The bifurcation of the $\alpha$-projection is studied, at which the uniqueness of the $\alpha$-approximation is broken.

Acceleration of the EM algorithm

Tue, 01 Feb 2000 00:00:00 +0000

Systems and Computers in Japan, vol. 31, no. 2, pp. 10–18

著者:

Shiro Ikeda

URL:

Abstract:

The EM algorithm is used for many applications, including the Boltzmann machine, stochastic Perceptron, and HMM. This algorithm gives an iterating procedure for calculating the MLE of stochastic models which have hidden random variables. It is simple, but the convergence is slow. We also have the ``Fisher scoring method.’’ Its convergence is faster, but the calculation load is heavy. We show that by using the EM algorithm recursively, we can connect these two methods and accelerate the EM algorithm. Also, Louis, Meng, and Rubin showed they can accelerate the EM algorithm, but our algorithm is simpler. We present some numerical simulations using our algorithm.

独立成分解析とは(第10回)–ノイズと独立成分解析–

Tue, 01 Feb 2000 00:00:00 +0000

Computer Today 3月号, pp. 60–65

著者:

池田思朗

キーワード:

独立成分分析

独立成分解析の信号処理への応用

Thu, 01 Jul 1999 00:00:00 +0000

計測自動制御学会「計測と制御」, vol. 38, no. 7, pp. 461–467

著者:

池田思朗

キーワード:

独立成分分析

URL:

Abstract:

独立成分解析 (ICA, Independent Component Analysis) は主成分分析 (PCA, Principal Compoenent Analysis) と同様，多次元信号の解析手法である．PCA では信号の 2 次の相関のみに注目し，それらを無相関にする変換を求める.これに対し ICA は高次の統計量，あるいは時間的な相関に基づく独立性により信号を分離する変換を求める．正規分布以外の確率分布に対しては一般に無相関と独立性とは一致しない．したがって PCA と ICA は異なる結果を与える．この ICA が近年注目されるようになったのは，問題の単純さとその応用の可能性からである．ICA では信号源が独立であるという仮定のみを置く．このことから Blind Source Separation とも呼ばれ，この仮定に基づいて信号を分離する．例えば脳計測によって得られたデータを考える.脳内では様々な部位が活動しており，それらが混合されて観これらが独立だと考えられれば ICA の仮定があてはまる．この他にも雑音の加わった画像，また複数の話者が同時に発声している信号を分離する問題などが挙げられる．ICA の手法を用いれば，これらが自動的に独立な成分として分離できるのである．本稿では近年盛んに研究されている ICA について問題の定式化，代表的な解法，応用の現状について述べる．

再帰的学習によるEMアルゴリズムの加速

Tue, 01 Dec 1998 00:00:00 +0000

電子情報通信学会論文誌, vol. J81-D-II, no. 12, pp. 2819–2827

著者:

池田思朗

キーワード:

EM アルゴリズム

URL:

Link

Abstract:

EM アルゴリズムはボルツマンマシンや確率的パーセプトロンなどの学習を始め，HMM やその他隠れた確率変数を持つ確率分布の学習に対して広く持ちいられている.このアルゴリズムは繰り返し演算により最尤推定を求めるものであり，計算量が少なく実現が容易だが，一般に収束が遅い．一方，統計学の分野で Fisher のスコアリング法と呼ばれる手法があり，これも同様のモデルに対して適用できる繰り返し演算である．スコアリング法は収束は速いが計算量が多く実現が難しい．本論文では EM アルゴリズムを再帰的に用いてスコアリング法を近似し，EM アルゴリズムを加速できることを示す．Louis や Meng and Rubin も同様のアプローチを行なっているが，本手法はそれらに比べ，計算量が少なく実現が容易である．計算機実験を交えて結果を示す．

HMMの構造探索による音素モデルの生成

Sun, 01 Jan 1995 00:00:00 +0000

電子情報通信学会論文誌, vol. J78-D-II, no. 1, pp. 10–18

著者:

池田思朗

キーワード:

EM アルゴリズム
モデル選択

URL:

Link

Abstract:

本論文では，HMM の構造決定のためのアルゴリズムを提案する．音声認識で用いられる HMM の構造は，多くの場合知識や経験に基づき決定されている．しかしながら，この問題は確率モデルの構造決定問題として扱うことができる．すなわち，赤池情報量規準 (AIC) などの尺度でモデルを評価し，最も良いモデルを選択するという方法で定式化できる.簡単な確率モデルにおいては，あらかじめ複数のモデルを用意し，最ゆう法でパラメタを推定した後に AIC 等で最適なモデルを選択すれば良い．一方，HMM のようにパラメタ推定のための計算量が多い場合，効率良く，少ないモデルに対してのパラメタ推定のみで済ませたい．そのために，HMM の状態数，あるいは状態遷移を一つづつ増やしていき，そのつどパラメタ推定を行ない，AIC でモデルを評価する方法をとり，これをモデル探索と呼ぶことにする．本アルゴリズムを用いてモデルを構成し，計算機上データによる実験，さらに音声データを用いて認識実験を行ない，データの統計的性質を反映したモデルがどのように構成されたかを調べ，本アルゴリズムを用いる効果を示す．

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