Curriculum Vitaes
Profile Information
- Affiliation
- Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency
- Degree
- 理学博士(中央大学)理学修士(中央大学)
- J-GLOBAL ID
- 201201017168289883
- researchmap Member ID
- 7000000018
Research Interests
2Research Areas
2Education
4-
- 2011
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- 2008
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- 2002
Committee Memberships
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2012
Papers
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Monthly Notices of the Royal Astronomical Society, 484(2) 2229-2233, Apr, 2019 Peer-reviewedWR 125 is considered to be a colliding-wind Wolf-Rayet binary (CWWB), from which the most recent infrared flux increase was reported between 1990 and 1993. We observed the object four times from 2016 November to 2017 May with Swift and XMM-Newton, and carried out a precise X-ray spectral study for the first time. There were hardly any changes in the fluxes and spectral shapes for half a year, and the absorption-corrected luminosity was 3.0 x 10(33) erg s(-1) in the range 0.5-10.0 keV at a distance of 4.1 kpc. The hydrogen column density was higher than that expected from the interstellar absorption, and thus the X-ray spectra were probably absorbed by the Wolf-Rayet (WR) wind. The energy spectrum was successfully modelled by a collisional equilibrium plasma emission, in which both the plasma and the absorbing wind have unusual elemental abundances particular to WR stars. In 1981, the Einstein satellite clearly detected X-rays from WR 125, whereas the ROSAT satellite hardly detected X-rays in 1991, when the binary was probably around the periastron passage. We discuss possible causes for the unexpectedly low soft X-ray flux near the periastron.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN, 70(6), Oct 1, 2018We present the results from the Hitomi Soft Gamma-ray Detector (SGD)<br /> observation of the Crab nebula. The main part of SGD is a Compton camera, which<br /> in addition to being a spectrometer, is capable of measuring polarization of<br /> gamma-ray photons. The Crab nebula is one of the brightest X-ray / gamma-ray<br /> sources on the sky, and, the only source from which polarized X-ray photons<br /> have been detected. SGD observed the Crab nebula during the initial test<br /> observation phase of Hitomi. We performed the data analysis of the SGD<br /> observation, the SGD background estimation and the SGD Monte Carlo simulations,<br /> and, successfully detected polarized gamma-ray emission from the Crab nebula<br /> with only about 5 ks exposure time. The obtained polarization fraction of the<br /> phase-integrated Crab emission (sum of pulsar and nebula emissions) is (22.1<br /> $\pm$ 10.6)% and, the polarization angle is 110.7$^o$ + 13.2 / $-$13.0$^o$ in<br /> the energy range of 60--160 keV (The errors correspond to the 1 sigma<br /> deviation). The confidence level of the polarization detection was 99.3%. The<br /> polarization angle measured by SGD is about one sigma deviation with the<br /> projected spin axis of the pulsar, 124.0$^o$ $\pm$0.1$^o$.
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Astrophysical Journal, Supplement Series, 238(2), Oct, 2018© 2018. The American Astronomical Society. All rights reserved.. We present the third MAXI/GSC catalog in the high Galactic latitude sky () based on the 7-year data from 2009 August 13 to 2016 July 31, complementary to that in the low Galactic latitude sky (|b| > 10°) (Hori et al. 2018). We compile 682 sources detected at significances of s D,4-10 keV ≥ 6.5 in the 4-10 keV band. A two-dimensional image fit based on the Poisson likelihood algorithm (C-statistics) is adopted for the detections and constraints on their fluxes and positions. The 4-10 keV sensitivity reaches ≈0.48 mCrab, or ≈5.9 × 10-12 erg cm-2 s-1, over half of the survey area. Compared with the 37-month Hiroi et al. (2013) catalog, which adopted a threshold of s D,4-10 keV ≥ 7, the source number increases by a factor of ∼1.4. The fluxes in the 3-4 keV and 10-20 keV bands are further estimated, and hardness ratios (HRs) are calculated using the 3-4 keV, 4-10 keV, 3-10 keV, and 10-20 keV band fluxes. We also make the 4-10 keV light curves in 1-year bins for all the sources and characterize their variabilities with an index based on a likelihood function and the excess variance. Possible counterparts are found from five major X-ray survey catalogs by Swift, Uhuru, RXTE, XMM-Newton, and ROSAT, as well as an X-ray galaxy cluster catalog (MCXC). Our catalog provides the fluxes, positions, detection significances, HRs, 1-year bin light curves, variability indices, and counterpart candidates.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN, 70(3), Jun, 2018 Peer-reviewed
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Journal of Astronomical Telescopes, Instruments, and Systems, 4(2), Apr, 2018 Peer-reviewed© The Authors. The Hitomi (ASTRO-H) mission is the sixth Japanese x-ray astronomy satellite developed by a large international collaboration, including Japan, USA, Canada, and Europe. The mission aimed to provide the highest energy resolution ever achieved at E > 2 keV, using a microcalorimeter instrument, and to cover a wide energy range spanning four decades in energy from soft x-rays to gamma rays. After a successful launch on February 17, 2016, the spacecraft lost its function on March 26, 2016, but the commissioning phase for about a month provided valuable information on the onboard instruments and the spacecraft system, including astrophysical results obtained from first light observations. The paper describes the Hitomi (ASTRO-H) mission, its capabilities, the initial operation, and the instruments/spacecraft performances confirmed during the commissioning operations for about a month.
Misc.
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Proceedings of Science, Jan 1, 2017© Copyright owned by the author(s) under the terms of the Creative Commons. Since the launch in 2009 August, with the unprecedentedly high sensitivity as an all-sky X-ray monitor, MAXI has caught more than a hundred of huge flares from stars. Most of them are from low-mass, active stars (RS CVn systems, an Algol system, dMe systems, a dKe system, Young Stellar Objects). With the total radiative energy of 1034–1039ergs, the MAXI detections have broken the record of the largest flaring magnitudes in each stellar categories. The enlarged sample of intense flares has enabled us to do systematic studies in various viewpoints. One of the studies is the discovery of a universal correlation between the flare duration and the intrinsic X-ray luminosity, which holds for 5 and 12 orders of magnitude in the duration and LX, respectively (Tsuboi et al. 2016). Here, we review the studies of stellar flares obtained with MAXI.
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Nov 4, 2015Colliding Wolf-Rayet (WR) winds produce thermal X-ray emission widely<br /> observed by X-ray telescopes. In wide WR+O binaries, such as WR 140, the X-ray<br /> flux is tied to the orbital phase, and is a direct probe of the winds'<br /> properties. In the Galactic center, $\sim$30 WRs orbit the super massive black<br /> hole (SMBH) within $\sim$10", leading to a smorgasbord of wind-wind collisions.<br /> To model the X-ray emission of WR 140 and the Galactic center, we perform 3D<br /> hydrodynamic simulations to trace the complex gaseous flows, and then carry out<br /> 3D radiative transfer calculations to compute the variable X-ray spectra. The<br /> model WR 140 RXTE light curve matches the data well for all phases except the<br /> X-ray minimum associated with periastron, while the model spectra agree with<br /> the RXTE hardness ratio and the shape of the Suzaku observations throughout the<br /> orbit. The Galactic center model of the Chandra flux and spectral shape match<br /> well in the region r$<$3", but the model flux falls off too rapidly beyond this<br /> radius.
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Suzaku-MAXI 2014: Expanding the Frontiers of the X-ray Universe, pp.pp220-221, Sep, 2014
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Suzaku-MAXI 2014: Expanding the Frontiers of the X-ray Universe, pp.pp208-209, Sep, 2014
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Suzaku-MAXI 2014: Expanding the Frontiers of the X-ray Universe, pp.pp164-165, Sep, 2014
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May 20, 2014Colliding wind binaries (CWBs) are unique laboratories for X-ray<br /> astrophysics. The massive stars in these systems possess powerful stellar winds<br /> with speeds up to $\sim$3000 km s$^{-1}$, and their collision leads to hot<br /> plasma (up to $\sim10^8$K) that emit thermal X-rays (up to $\sim$10 keV). Many<br /> X-ray telescopes have observed CWBs, including Suzaku, and our work aims to<br /> model these X-ray observations. We use 3D smoothed particle hydrodynamics (SPH)<br /> to model the wind-wind interaction, and then perform 3D radiative transfer to<br /> compute the emergent X-ray flux, which is folded through X-ray telescopes'<br /> response functions to compare directly with observations. In these proceedings,<br /> we present our models of Suzaku observations of the multi-year-period, highly<br /> eccentric systems $\eta$ Carinae and WR 140. The models reproduce the<br /> observations well away from periastron passage, but only $\eta$ Carinae's X-ray<br /> spectrum is reproduced at periastron; the WR 140 model produces too much flux<br /> during this more complicated phase.
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Proceedings of SPIE - The International Society for Optical Engineering, 9144, 2014© 2014 SPIE. The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly successful X-ray missions developed by the Institute of Space and Astronautical Science (ISAS), with a planned launch in 2015. The ASTRO-H mission is equipped with a suite of sensitive instruments with the highest energy resolution ever achieved at E > 3 keV and a wide energy range spanning four decades in energy from soft X-rays to gamma-rays. The simultaneous broad band pass, coupled with the high spectral resolution of ΔE ≤ 7 eV of the micro-calorimeter, will enable a wide variety of important science themes to be pursued. ASTRO-H is expected to provide breakthrough results in scientific areas as diverse as the large-scale structure of the Universe and its evolution, the behavior of matter in the gravitational strong field regime, the physical conditions in sites of cosmic-ray acceleration, and the distribution of dark matter in galaxy clusters at different redshifts.
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Space Telescopes and Instrumentation 2012: Ultraviolet to Gamma Ray. Proceedings of the SPIE, 8443, Sep, 2012
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SUZAKU 2011: EXPLORING THE X-RAY UNIVERSE: SUZAKU AND BEYOND, 1427 296-297, 2012We present results of spectral studies of two Wolf-Rayet colliding wind binaries (WR 140 and WR 30a), using the data obtained by the Suzaku and XMM-Newton satellites. WR 140 is one of the best known examples of a Wolf-Rayet star. We executed the Suzaku X-ray observations at four different epochs around periastron passage in Jan. 2009 to understand the W-R stellar wind as well as the wind-wind collision shocks. We detected hard X-ray excess in the HXD band (> 10 key) for the first time from a W-R binary. The luminosity of the dominant, high temperature component is not inversely proportional to the distance between the two stars. WR 30a is the rare WO-type W-R binary. We executed XMM-Newton observations and detected X-ray emission for the first time. The broad-band spectrum was well-fitted with double-absorption model. The hard X-ray emission was heavily absorbed. This can be interpreted that the hard X-ray emitting plasma exist near WO star.
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DEATH OF MASSIVE STARS: SUPERNOVAE AND GAMMA-RAY BURSTS, 279(279) 351-352, 2012By monitoring WC7 and the O5.5 binary WR 140 with the Suzaku telescope, we demonstrate a new method to measure the mass loss rates of both stars. By using the absorption column density, we found a mass-loss rate for the WC7 component : M-wc7 approximate to 1.2 x 10(-5)M circle dot yr(-1). We also measured the mass-loss rate of the companion O component using a luminosity variation in phases: M-O5.5 approximate to 5 x 10(-7)M circle dot yr(-1).
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Proceedings of the International Astronomical Union, 10(16) 51-79, 2012Recent studies have claimed the existence of very massive stars (VMS) up to 300 M⊙ in the local Universe. As this finding may represent a paradigm shift for the canonical stellar upper-mass limit of 150 M⊙, it is timely to discuss the status of the data, as well as the far-reaching implications of such objects. We held a Joint Discussion at the General Assembly in Beijing to discuss (i) the determination of the current masses of the most massive stars, (ii) the formation of VMS, (iii) their mass loss, and (iv) their evolution and final fate. The prime aim was to reach broad consensus between observers and theorists on how to identify and quantify the dominant physical processes.
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Proceedings of SPIE - The International Society for Optical Engineering, 8443, 2012The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly successful X-ray missions initiated by the Institute of Space and Astronautical Science (ISAS). ASTRO-H will investigate the physics of the highenergy universe via a suite of four instruments, covering a very wide energy range, from 0.3 keV to 600 keV. These instruments include a high-resolution, high-Throughput spectrometer sensitive over 0.3-12 keV with high spectral resolution of ?E 5 7 eV, enabled by a micro-calorimeter array located in the focal plane of thin-foil X-ray optics; hard X-ray imaging spectrometers covering 5-80 keV, located in the focal plane of multilayer-coated, focusing hard X-ray mirrors; a wide-field imaging spectrometer sensitive over 0.4-12 keV, with an X-ray CCD camera in the focal plane of a soft X-ray telescope; and a non-focusing Compton-camera type soft gamma-ray detector, sensitive in the 40-600 keV band. The simultaneous broad bandpass, coupled with high spectral resolution, will enable the pursuit of a wide variety of important science themes. © 2012 SPIE.
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AIP Conference Proceedings, 1279 363-365, Oct, 2010WR 140 is one of the best known examples of a Wolf-Rayet stars. We executed the Suzaku X-ray observations at four different epochs around periastron passage in Jan. 2009 to understand the W-R stellar wind as well as the wind-wind collision shocks. The column density at periastron is about 30 times higher than that at pre-periastron, which can be explained as self-absorption by the Wolf-Rayet wind. The spectra are dominated by a line and continuum emission from a optically thin-thermal plasma. The strong Ne-K lines are evidence that the thermal plasma is shock-heated W-R wind materials by the interaction with the wind from the companion O star. We present the parameters of the wind, such as a mass-loss rate, which were calculated with the absorption and line emission in the spectra. © 2010 American Institute of Physics.
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AIP Conference Proceedings, 1248 9-12, Jul, 2010We report the preliminary results of the Suzaku observations of the W-R binary WR 140 (WC7+O5I). We executed the observations at four different epochs around periastron passage in Jan. 2009 to understand the W-R stellar wind as well as the wind-wind collision shocks. The total exposure was 210 ksec. We detected hard X-ray excess in the HXD band (>10 keV) for the first time from a W-R binary. Another notable discovery was a soft component which is not absorbed even by the dense wind. The spectra can be fitted by three different components; one is for the stationary cool component with kT ∼0.1 keV, one for a dominant high temperature component with kT ∼3 keV, and one for the hardest power-low component with Γ∼2. The column density at periastron is 30 times higher than that at pre-periastron, which can be explained as self-absorption by the W-R wind. The emission measure of the dominant, high temperature component is not inversely proportional to the distance between the two stars. © 2010 American Institute of Physics.
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JAXA Special Publication: The Energetic Cosmos: from Suzaku to ASTRO-H, 198-199, Jan, 2010
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Active OB-Stars: Laboratories for Stellar and Circumstellar Physics, 361 500-502, Mar, 2007
Presentations
68Professional Memberships
3Works
1Research Projects
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科学研究費補助金 若手研究(B), Apr, 2016 - Mar, 2019
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科学研究費補助金 特別研究促進費, Apr, 2009 - Mar, 2011
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2005
