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
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- 2011
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- 2008
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- 2002
Committee Memberships
1-
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
Presentations
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Variable Galactic Gamma- Ray Sources (IV), Jul 6, 2017 Invited
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International Workshop on Wolf-Rayet Stars, Jun, 2015
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The 40th COSPAR Scientific Assembly E1.3, Aug, 2014
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Suzaku-MAXI 2014 - Expanding the Frontiers of the X-ray Universe, Feb, 2014
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Multi-Messengers from Core-Collapse Supernovae, Dec, 2013
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1st Annual Symposium on "New Developments in Astrophysics Through Multi-Messenger Observations of Gravitational Wave Sources ", Mar, 2013
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XXVIII IAU General Assembly JD2, Aug, 2012
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Formations of Compact Objects: from the cradle to the grave, Mar, 2012
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Suzaku 2011 - Exploring the X-ray Universe: Suzaku and Beyond, Jul, 2011
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The multi-wavelength view of Hot, Massive Stars, Jul, 2010
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X-RAY ASTRONOMY 2009:PRESENT STATUS, MULTI-WAVELENGTH APPROACH AND FUTURE PERSPECTIVES, Sep, 2009
Professional 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
