研究者業績
基本情報
- 所属
- 国立研究開発法人宇宙航空研究開発機構 宇宙科学研究所 宇宙物理学研究系 教授総合研究大学院大学 先端学術院 宇宙科学コース 教授東京科学大学 理学院物理学系物理学コース 特定教授関西学院大学 大学院理工学研究科 客員教授
- 学位
- 理学博士(東京大学)
- J-GLOBAL ID
- 200901025041369206
- researchmap会員ID
- 1000144439
専門はX線天文学。特に、中性子星やブラックホールを含むX線連星の観測的研究および衛星搭載X線CCDカメラの開発研究。
受賞
1-
1996年
論文
231-
The Astrophysical Journal Letters 982(1) L5-L5 2025年3月12日Abstract We present XRISM Resolve observations of the core of the hot, relaxed galaxy cluster Abell 2029 (A2029). We find that the line-of-sight bulk velocity of the intracluster medium (ICM) within the central 180 kpc is at rest with respect to the brightest cluster galaxy, with a 3σ upper limit of ∣v bulk∣ < 100 km s−1. We robustly measure the field-integrated ICM velocity dispersion to be σ v = 169 ± 10 km s−1, obtaining similar results for both single-temperature and two-temperature plasma models to account for the cluster cool core. This result, if ascribed to isotropic turbulence, implies a subsonic ICM with Mach number and a nonthermal pressure fraction of 2.6 ± 0.3%. The turbulent velocity is similar to what was measured in the core of the Perseus cluster by Hitomi, but here in a more massive cluster with an ICM temperature of 7 keV, the limit on the nonthermal pressure fraction is even more stringent. Our result is consistent with expectations from simulations of relaxed clusters, but it is on the low end of the predicted distribution, indicating that A2029 is an exceptionally relaxed cluster with no significant impacts from either a recent minor merger or active galactic nucleus activity.
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Nature 638(8050) 365-369 2025年2月12日
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Publications of the Astronomical Society of Japan 2024年12月26日Abstract Sagittarius A East is a supernova remnant with a unique surrounding environment, as it is located in the immediate vicinity of the supermassive black hole at the Galactic center, Sagittarius A$^{*}$. The X-ray emission of the remnant is suspected to show features of overionized plasma, which would require peculiar evolutionary paths. We report on the first observation of Sagittarius A East with the X-Ray Imaging and Spectroscopy Mission (XRISM). Equipped with a combination of a high-resolution microcalorimeter spectrometer and a large field-of-view CCD imager, we for the first time resolved the Fe xxv K-shell lines into fine structure lines and measured the forbidden-to-resonance intensity ratio to be $1.39 \pm 0.12$, which strongly suggests the presence of overionized plasma. We obtained a reliable constraint on the ionization temperature just before the transition into the overionization state, of $\gt\! 4\:$keV. The recombination timescale was constrained to be $\lt\! 8 \times 10^{11} \:$cm$^{-3}\:$s. The small velocity dispersion of $109 \pm 6\:$km$\:$s$^{-1}$ indicates a low Fe ion temperature $\lt\! 8\:$keV and a small expansion velocity $\lt\! 200\:$km$\:$s$^{-1}$. The high initial ionization temperature and small recombination timescale suggest that either rapid cooling of the plasma via adiabatic expansion from dense circumstellar material or intense photoionization by Sagittarius A$^{*}$ in the past may have triggered the overionization.
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The Astrophysical Journal Letters 977(2) L34-L34 2024年12月11日Abstract The X-ray binary system Cygnus X-3 (4U 2030+40, V1521 Cyg) is luminous but enigmatic owing to the high intervening absorption. High-resolution X-ray spectroscopy uniquely probes the dynamics of the photoionized gas in the system. In this Letter, we report on an observation of Cyg X-3 with the XRISM/Resolve spectrometer, which provides unprecedented spectral resolution and sensitivity in the 2–10 keV band. We detect multiple kinematic and ionization components in absorption and emission whose superposition leads to complex line profiles, including strong P Cygni profiles on resonance lines. The prominent Fe xxv Heα and Fe xxvi Lyα emission complexes are clearly resolved into their characteristic fine-structure transitions. Self-consistent photoionization modeling allows us to disentangle the absorption and emission components and measure the Doppler velocity of these components as a function of binary orbital phase. We find a significantly higher velocity amplitude for the emission lines than for the absorption lines. The absorption lines generally appear blueshifted by ∼−500–600 km s−1. We show that the wind decomposes naturally into a relatively smooth and large-scale component, perhaps associated with the background wind itself, plus a turbulent, denser structure located close to the compact object in its orbit.
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Publications of the Astronomical Society of Japan 2024年10月10日Abstract We present an initial analysis of the X-Ray Imaging and Spectroscopy Mission (XRISM) first-light observation of the supernova remnant (SNR) N 132D in the Large Magellanic Cloud. The Resolve microcalorimeter has obtained the first high-resolution spectrum in the 1.6–10 keV band, which contains K-shell emission lines of Si, S, Ar, Ca, and Fe. We find that the Si and S lines are relatively narrow, with a broadening represented by a Gaussian-like velocity dispersion of $\sigma _v \sim 450$ km s$^{-1}$. However, the Fe He$\alpha$ lines are substantially broadened with $\sigma _v \sim 1670$ km s$^{-1}$. This broadening can be explained by a combination of the thermal Doppler effect due to the high ion temperature and the kinematic Doppler effect due to the SNR expansion. Assuming that the Fe He$\alpha$ emission originates predominantly from the supernova ejecta, we estimate the reverse shock velocity at the time when the bulk of the Fe ejecta were shock heated to be $-1000 \lesssim V_{\rm rs}$ (km s$^{-1}$) $\lesssim 3300$ (in the observer frame). We also find that Fe Ly$\alpha$ emission is redshifted with a bulk velocity of $\sim 890$ km s$^{-1}$, substantially larger than the radial velocity of the local interstellar medium surrounding N 132D. These results demonstrate that high-resolution X-ray spectroscopy is capable of providing constraints on the evolutionary stage, geometry, and velocity distribution of SNRs.
MISC
201-
X-RAY AND GAMMA-RAY TELESCOPES AND INSTRUMENTS FOR ASTRONOMY, PTS 1 AND 2 4851 1071-1079 2003年
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PASJ : publications of the Astronomical Society of Japan 54(3) 373-386 2002年6月25日
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X-RAY AND GAMMA-RAY INSTRUMENTATION FOR ASTRONOMY XII 4497 158-165 2002年
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PASJ : publications of the Astronomical Society of Japan 53(6) 1171-1177 2001年12月25日
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Astrophysical Journal, Supplement Series 131 571-591 2000年12月1日
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ASTROPHYSICAL JOURNAL 543(2) L145-L148 2000年11月
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Astrophys.J. 539 (2000) 413; Erratum-ibid. 651 (2006) 615-616 2000年3月16日We have discovered errors in the calculation of some of the Einstein<br /> coefficients in Table 5 and some plots in Figure 3. Due to the errors, the<br /> square-root section of the curves of growth of Fe xxvi Ka and Kb, and Ni xxviii<br /> Ka in Figure 3 were a few times underestimated. We correct Table 5 and re-plot<br /> Figure 3 together with the unaffected curves. The program to calculate the<br /> corrected curves of growth is available at<br /> http://www.hp.phys.titech.ac.jp/kotani/cog/index.html
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Astrophys.J.535:632,2000 535(2) 632-643 2000年1月3日Studies were made of ASCA spectra of seven ultra-luminous compact X-ray<br /> sources (ULXs) in nearby spiral galaxies; M33 X-8 (Takano et al. 1994), M81 X-6<br /> (Fabbiano 1988b; Kohmura et al. 1994; Uno 1997), IC 342 Source 1 (Okada et al.<br /> 1998), Dwingeloo 1 X-1 (Reynolds et al. 1997), NGC 1313 Source B (Fabbiano &<br /> Trinchieri 1987; Petre et al. 1994), and two sources in NGC 4565 (Mizuno et al.<br /> 1999). With the 0.5--10 keV luminosities in the range 10^{39-40} ergs/s, they<br /> are thought to represent a class of enigmatic X-ray sources often found in<br /> spiral galaxies. For some of them, the ASCA data are newly processed, or the<br /> published spectra are reanalyzed. For others, the published results are quoted.<br /> The ASCA spectra of all these seven sources have been described successfully<br /> with so called multi-color disk blackbody (MCD) emission arising from<br /> optically-thick standard accretion disks around black holes. Except the case of<br /> M33 X-8, the spectra do not exhibit hard tails. For the source luminosities not<br /> to exceed the Eddington limits, the black holes are inferred to have rather<br /> high masses, up to ~100 solar masses. However, the observed innermost disk<br /> temperatures of these objects, Tin = 1.1--1.8 keV, are too high to be<br /> compatible with the required high black-hole masses, as long as the standard<br /> accretion disks around Schwarzschild black holes are assumed. Similarly high<br /> disk temperatures are also observed from two Galactic transients with<br /> superluminal motions, GRO 1655-40 and GRS 1915+105. The issue of unusually high<br /> disk temperature may be explained by the black hole rotation, which makes the<br /> disk get closer to the black hole, and hence hotter.
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BROAD BAND X-RAY SPECTRA OF COSMIC SOURCES 25(3-4) 669-672 2000年
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BROAD BAND X-RAY SPECTRA OF COSMIC SOURCES 25(3-4) 391-394 2000年
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BROAD BAND X-RAY SPECTRA OF COSMIC SOURCES 25(3-4) 375-378 2000年
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Astronomy and Astrophysics 343 197-201 1999年12月1日
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PASJ : publications of the Astronomical Society of Japan 51(4) 519-524 1999年
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PASJ : publications of the Astronomical Society of Japan 50(6) 667-673 1998年12月1日
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PASJ : publications of the Astronomical Society of Japan 50(6) 611-619 1998年12月1日
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PASJ : publications of the Astronomical Society of Japan 50(2) 249-255 1998年4月25日
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X-RAY TIMING AND COSMIC GAMMA RAY BURSTS 22(7) 961-964 1998年
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Proceedings of SPIE - The International Society for Optical Engineering 3445 278-290 1998年 査読有り
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Publications of the Astronomical Society of Japan 49(6) 653-658 1997年12月1日
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Astronomy and Astrophysics 322 857-867 1997年6月20日
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東海大学紀要. 理学部 32 125-133 1997年3月An eclipsing X-ray binary pulsar, Centaurus X-3 was observed with the ASCA satellite on Februarly 1-2 1995,during a non-eclipse phase of 0.11 to 0.81. We found that the X-ray pulse profiles observed with ASCA change in shape and amplitude according with the orbital phase. The three K_α lines at 6.4,6.67,and 6.96 keV from neutral, He-like, and H-like ironions, respectively, could be resolved in the observed energy spectrum owing to the high energy resolution of the CCD cameras on board ASCA. We found that the intensity of the 6.4 keV line changes with pulse phase. Distribution and ionization degree of matter surrounding the neutron star are discussed based on this result.
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PROCEEDINGS OF THE FOURTH COMPTON SYMPOSIUM, PTS 1 AND 2 (410) 844-848 1997年
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Astrophysical Journal 489(1) 272-283 1997年
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IEEE Transactions on Nuclear Science 44(3) 847-853 1997年
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1996 IEEE NUCLEAR SCIENCE SYMPOSIUM - CONFERENCE RECORD, VOLS 1-3 1 261-262 1997年
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ASTROPHYSICAL JOURNAL 437(1) 449-457 1994年12月
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ASTROPHYSICAL JOURNAL 436(2) 871-874 1994年12月
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ASTROPHYSICAL JOURNAL 427(1) 400-405 1994年5月
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ASTROPHYSICAL JOURNAL 422(2) 799-809 1994年2月
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ASTROPHYSICAL JOURNAL 421(2) 738-752 1994年2月
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 44(6) 633-640 1992年
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 43(4) L43-L50 1991年
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ASTROPHYSICAL JOURNAL 361(2) 514-526 1990年10月
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ASTROPHYSICAL JOURNAL 351(1) L13-L16 1990年3月
所属学協会
4-
2000年1月 - 現在
共同研究・競争的資金等の研究課題
15-
日本学術振興会 科学研究費助成事業 基盤研究(C) 2019年4月 - 2023年3月
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日本学術振興会 科学研究費助成事業 新学術領域研究(研究領域提案型) 2012年6月 - 2017年3月
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日本学術振興会 科学研究費助成事業 2012年4月 - 2015年3月
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日本学術振興会 科学研究費助成事業 基盤研究(B) 2010年4月 - 2013年3月
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日本学術振興会 科学研究費助成事業 特別研究員奨励費 2005年 - 2007年
● 指導学生等の数
1-
年度2021年度(FY2021)修士課程学生数2連携大学院制度による学生数2学術特別研究員数1
● 専任大学名
1-
専任大学名総合研究大学院大学(SOKENDAI)