Dept. of Space Astronomy and Astrophysics
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.
203Professional 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)
