Curriculum Vitaes
Profile Information
- Affiliation
- Professor, Institute of Space and Astronautical Science, High Energy Astrophysics, Japan Aerospace Exploration AgencyProfessor, Graduate Institute for Advanced Studies, Space and Astronautical Science program, The Graduate University for Advanced Studies, SOKENDAIVisiting Professor, School of Science, Institute of Science TokyoVisiting professor, Graduate School of Science and Technology, Kwansei Gakuin University
- Degree
- PhD(The University of Tokyo)
- J-GLOBAL ID
- 200901025041369206
- researchmap Member ID
- 1000144439
My research field is X-ray astronomy, especially observational studies of X-ray binaries including neutron stars or black holes, and development of X-ray CCD cameras for X-ray astronomy satellites.
Research Interests
6Research Areas
2Awards
1-
1996
Papers
246-
The Astrophysical Journal, 998(2) 210-210, Feb 11, 2026Abstract The XRISM/Resolve microcalorimeter directly measured the gas velocities in the core of the Virgo Cluster, the closest example of active galactic nucleus (AGN) feedback in a cluster. This proximity allows us to resolve the kinematic impact of feedback on scales down to 5 kpc. Our spectral analysis reveals a high velocity dispersion of km s −1 near the AGN, which steeply declines to ∼60 km s −1 between 5 and 25 kpc in the northwest direction. The observed line-of-sight bulk velocity in all regions is broadly consistent with the central galaxy, M87, with a mild trend toward blueshifted motions at larger radii. Systematic uncertainties have been carefully assessed and do not affect the measurements. The central velocities, if attributed entirely to isotropic turbulence, correspond to a transonic intracluster medium at sub-6 kpc scales with 3D Mach number and a nonthermal pressure fraction of . Simple models of weak shocks and sound waves and calculations assuming isotropic turbulence both support the hypothesis that the velocity field reflects a mix of shock-driven expansion and turbulence. Compared to other clusters observed by XRISM to date, M87’s central region stands out as the most kinematically disturbed, exhibiting both the highest velocity dispersion and the largest 3D Mach number, concentrated at the smallest physical scales.
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Nature, 650(8101) 309-313, Jan 28, 2026
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NATURE ASTRONOMY, 10(1), Jan, 2026
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The Astrophysical Journal Letters, 994(1) L28-L28, Nov 18, 2025Abstract We stack 3.75 Ms of early XRISM Resolve observations of 10 galaxy clusters to search for unidentified spectral lines in the E = 2.5–15 keV band (rest frame), including the E = 3.5 keV line reported in earlier low spectral resolution studies of cluster samples. Such an emission line may originate from the decay of the sterile neutrino, a warm dark matter (DM) candidate. No unidentified lines are detected in our stacked cluster spectrum, with the 3 σ upper limit on the m s ∼ 7.1 keV DM particle decay rate (which corresponds to an E = 3.55 keV emission line) of Γ ∼ 1.0 × 10 −27 s −1 . This upper limit is 3–4 times lower than the one derived by Hitomi Collaboration from the Perseus observation but still 5 times higher than the XMM-Newton detection reported by E. Bulbul et al. in the stacked cluster sample. XRISM Resolve, with its high spectral resolution but small field of view, may reach the sensitivity needed to test the XMM-Newton cluster sample detection by combining several years worth of future cluster observations.
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Publications of the Astronomical Society of Japan, 77(6) 1278-1289, Nov 17, 2025Abstract We present results from XRISM/Resolve observations of the core of the galaxy cluster Abell 2319, focusing on its kinematic properties. The intracluster medium (ICM) exhibits temperatures of approximately 8 keV across the core, with a prominent cold front and a high-temperature region ($\sim$11 keV) in the north-west. The average gas velocity in the $3{^{\prime } } \times$ $4 {^{\prime } }$ region around the brightest cluster galaxy (BCG) covered by two Resolve pointings is consistent with that of the BCG to within 40 km s$^{-1}$ and we found modest average velocity dispersion of 230–250 km s$^{-1}$. On the other hand, spatially resolved spectroscopy reveals interesting variations. A blueshift of up to $\sim$230 km s$^{-1}$ is observed around the east edge of the cold front, where the gas with the lowest specific entropy is found. The region further south inside the cold front shows only a small velocity difference from the BCG; however, its velocity dispersion is enhanced to $\sim$400 km s$^{-1}$, implying the development of turbulence. These characteristics indicate that we are observing sloshing motion with some inclination angle following BCG and that gas phases with different specific entropy participate in sloshing with their own velocities, as expected from simulations. No significant evidence for a high-redshift ICM component associated with the subcluster Abell 2319B was found in the region covered by the current Resolve pointings. These results highlight the importance of sloshing and turbulence in shaping the internal structure of Abell 2319. Further deep observations are necessary to better understand the mixing and turbulent processes within the cluster.
Misc.
203-
X-RAY AND GAMMA-RAY TELESCOPES AND INSTRUMENTS FOR ASTRONOMY, PTS 1 AND 2, 4851 1071-1079, 2003
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Publications of the Astronomical Society of Japan, 54(3) 373-386, Jun 25, 2002
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X-RAY AND GAMMA-RAY INSTRUMENTATION FOR ASTRONOMY XII, 4497 158-165, 2002
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Publications of the Astronomical Society of Japan, 53(6) 1171-1177, Dec 25, 2001
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Astrophysical Journal, Supplement Series, 131 571-591, Dec 1, 2000
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ASTROPHYSICAL JOURNAL, 543(2) L145-L148, Nov, 2000
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Astrophys.J. 539 (2000) 413; Erratum-ibid. 651 (2006) 615-616, Mar 16, 2000We 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, Jan 3, 2000Studies 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
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BROAD BAND X-RAY SPECTRA OF COSMIC SOURCES, 25(3-4) 391-394, 2000
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BROAD BAND X-RAY SPECTRA OF COSMIC SOURCES, 25(3-4) 375-378, 2000
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Astronomy and Astrophysics, 343 197-201, Dec 1, 1999
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Meeting abstracts of the Physical Society of Japan, 54(2) 81-81, Sep 13, 1999
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Meeting abstracts of the Physical Society of Japan, 54(1) 362-362, Mar 15, 1999
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Publications of the Astronomical Society of Japan, 51(4) 519-524, 1999
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Publications of the Astronomical Society of Japan, 50(6) 667-673, Dec 1, 1998
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Publications of the Astronomical Society of Japan, 50(6) 611-619, Dec 1, 1998
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Meeting abstracts of the Physical Society of Japan, 53(2) 83-83, Sep 5, 1998
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Publications of the Astronomical Society of Japan, 50(2) 249-255, Apr 25, 1998
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X-RAY TIMING AND COSMIC GAMMA RAY BURSTS, 22(7) 961-964, 1998
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日本天文学会年会講演予稿集, 1998 207, 1998
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Proceedings of SPIE - The International Society for Optical Engineering, 3445 278-290, 1998 Peer-reviewed
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Publications of the Astronomical Society of Japan, 49(6) 653-658, Dec 1, 1997
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Meeting abstracts of the Physical Society of Japan, 52(2) 78-78, Sep 2, 1997
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Meeting abstracts of the Physical Society of Japan, 52(2) 78-78, Sep 2, 1997
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Astronomy and Astrophysics, 322 857-867, Jun 20, 1997
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日本物理學會誌, 52(6) 450-451, Jun 5, 1997
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Meeting abstracts of the Physical Society of Japan, 52(1) 83-83, Mar 17, 1997
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Proceedings of the School of Science of Tokai University, 32 125-133, Mar, 1997An 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
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Astrophysical Journal, 489(1) 272-283, 1997
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IEEE Transactions on Nuclear Science, 44(3) 847-853, 1997
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1996 IEEE NUCLEAR SCIENCE SYMPOSIUM - CONFERENCE RECORD, VOLS 1-3, 1 261-262, 1997
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ASTROPHYSICAL JOURNAL, 437(1) 449-457, Dec, 1994
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ASTROPHYSICAL JOURNAL, 436(2) 871-874, Dec, 1994
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ASTROPHYSICAL JOURNAL, 427(1) 400-405, May, 1994
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ASTROPHYSICAL JOURNAL, 422(2) 799-809, Feb, 1994
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ASTROPHYSICAL JOURNAL, 421(2) 738-752, Feb, 1994
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN, 44(6) 633-640, 1992
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN, 43(4) L43-L50, 1991
Professional Memberships
4-
Jan, 2000 - Present
Research Projects
15-
Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C), Japan Society for the Promotion of Science, Apr, 2019 - Mar, 2023
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Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area), Japan Society for the Promotion of Science, Jun, 2012 - Mar, 2017
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Grants-in-Aid for Scientific Research, Japan Society for the Promotion of Science, Apr, 2012 - Mar, 2015
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Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B), Japan Society for the Promotion of Science, Apr, 2010 - Mar, 2013
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科学研究費助成事業 特別研究員奨励費, 日本学術振興会, 2005 - 2007
● 指導学生等の数
1-
Fiscal Year2021年度(FY2021)Master’s program3Students under Cooperative Graduate School System3JSPS Research Fellowship (Young Scientists)1
● 専任大学名
1-
Affiliation (university)総合研究大学院大学（SOKENDAI)
