宇宙物理学研究系
Profile Information
- Affiliation
- Professor, Institute of Space and Astronautical Science, Japan Aerospace Exploration AgencyProfessor, Graduate School of Science Department of Physics, The University of TokyoCollege of Science and Engineering, Aoyama Gakuin UniversityNational Institute for Fusion Science
- Degree
- PhD(Mar, 2008, Kyoto University)
- Contact information
- yamaguchi.hiroya
jaxa.jp - Researcher number
- 00513467
- J-GLOBAL ID
- 201801007525282778
- researchmap Member ID
- B000340695
- External link
主な研究テーマ・プロジェクト業務
宇宙プラズマ現象、Ｘ線連星、Ia型超新星、超新星残骸、銀河団、原子過程、実験室宇宙物理学
XRISM プロジェクトサイエンティスト
下記の業績リストは不完全です。「論文」は主要論文のみ、「講演・口頭発表等」は最近の招待講演のみリストしています。
座右の銘
努力して運を待て（仁科芳雄） 努力を続けていれば運が向いた時に見逃さないって意味だと思う。運は誰にでも同じ頻度で巡ってくる。それに気づき活かせるかは本人の努力次第。
疑行無名、疑事無功（『戦国策』） 後から迷走しないように達成目標と実施計画を明確にすべしって意味だと思う。目的意識もなく仕事に取り掛かるから、行き当たりばったりになり良い成果が挙がらない。
人、城を頼らば、城、人を捨せん（織田信長） プロジェクトがあれば何とかなると考えていたらプロジェクトが頓挫したときに自力で起き上がれないって意味だと思う。この懸念は2016年に現実のものとなった。
Research Interests
6Research Areas
2Research History
12-
Jun, 2025 - Present
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May, 2025 - Present
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Apr, 2023 - Present
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Apr, 2019 - Jun, 2025
Education
3-
Apr, 2003 - Mar, 2008
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Apr, 1999 - Mar, 2003
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Apr, 1996 - Mar, 1999
Committee Memberships
8-
Apr, 2023 - Present
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Apr, 2022 - Present
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May, 2021 - Present
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Oct, 2018 - Present
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Jun, 2021 - Mar, 2026
Awards
9Papers
61-
Publications of the Astronomical Society of Japan, 78(1) 174-184, Jan 23, 2026Abstract We present a spatially resolved high-resolution X-ray spectroscopy of the supernova remnant DEM L71 using the Reflection Grating Spectrometer (RGS) aboard XMM-Newton. Because of the large dispersion angle of the RGS, we are able to resolve individual emission lines and examine their spatial distributions within this moderately extended remnant. We derive line fluxes across different regions of DEM L71 and perform quantitative plasma diagnostics. Our analysis reveals that some regions have high forbidden-to-resonance ratios of O vii He$\alpha$ lines, suggesting a non-negligible contribution from additional physical processes, such as charge exchange and/or resonance scattering. Our results demonstrate that the RGS has potential to serve as an outstanding X-ray imaging spectrometer for moderately diffuse objects.
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Publications of the Astronomical Society of Japan, 77(Supplement_1) S86-S95, Jun 16, 2025Abstract To understand physical processes such as mass transfer and binary evolution in X-ray binaries, the orbital parameters of the system are fundamental and crucial information. Cygnus X-3 is a high-mass X-ray binary composed of a compact object of unknown nature and a Wolf–Rayet star, which is of great interest in the context of wind-fed mass accretion and binary evolution. Here we present XRISM/Resolve high-resolution spectroscopy, focusing on the Fe Ly$\alpha$ lines when the source was in its hypersoft state. We perform an orbital phase-resolved spectral analysis of the lines to study the orbital modulation of the emission and absorption lines. It is found that the emission lines reflect the orbital motion of the compact object whose estimated velocity amplitude is $430^{+150}_{-140}$ km s$^{-1}$, while the absorption lines show a variation that can be interpreted as originating from the stellar wind. We discuss possible mass ranges for the binary components using the mass function with the estimated value of the velocity amplitude in this work, combined with the relation between the mass-loss rate and the orbital period derivative and the empirical mass and mass-loss rate relation for Galactic Wolf–Rayet stars. They are constrained to be (1.3–5.1) and (9.3–12) M$_\odot$, respectively, for the assumed inclination angle of $i =25^\circ$, and become more relaxed, (1.3–24) and (9.3–16) M$_\odot$, for $i = 35^\circ$. Thus, it remains unclear whether the system harbors a black hole or a neutron star.
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Publications of the Astronomical Society of Japan, 77(Supplement_1) S131-S143, May 28, 2025Abstract Supernova remnants (SNRs) provide crucial information on the still poorly understood mechanism of supernova explosion. Here we present XRISM high-resolution spectroscopy of the intermediate-mass-element (IME) ejecta in the SNR Cas A to determine their velocity distribution and thermal properties. The XRISM/Resolve spectrum in the 1.75–2.95 keV band extracted from each $1^{\prime } \times 1^{\prime }$ region in the south-east and north-west rims is fitted with a model consisting of two-component plasmas in non-equilibrium ionization with different radial velocities and ionization timescales. It is found that the more highly ionized component has a larger radial velocity, suggesting that this component is distributed in the outer layer and thus has been heated by the SNR reverse shock earlier. We also perform proper motion measurement of the highly ionized component (represented by the Si xiv Ly$\alpha$ emission), using archival Chandra data, to reconstruct the three-dimensional velocity of the outermost IME ejecta. The pre-shock (free expansion) velocity of these ejecta is estimated to range from 2400 to 7100 km s$^{-1}$, based on the thermal properties and the bulk velocity of the shocked ejecta. These velocities are consistent with theoretical predictions for a Type IIb supernova, in which the progenitor’s hydrogen envelope is largely stripped before the explosion. Furthermore, we find a substantial asymmetry in the distribution of the free expansion velocities, with the highest value toward the direction opposite to the proper motion of the neutron star (NS). This indicates a physical association between the asymmetric supernova explosion and NS kick.
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Publications of the Astronomical Society of Japan, 77(Supplement_1) S188-S192, May 14, 2025Abstract XRISM has delivered one of its first light observations on N 132D, the X-ray brightest supernova remnant in the Large Magellanic Cloud. Utilizing 193 ks of high-resolution X-ray spectroscopy data, we conduct a comprehensive search for charge exchange emission. By incorporating a charge exchange model into our spectral analysis, we observe an improvement in the fits of two weak features at 2.41 and 2.63 keV. These features, with a combined significance of 99.6%, are consistent with transitions from highly ionized silicon ions in high Rydberg states, which are unique indicators of charge exchange. Our analysis constrains the charge exchange flux to no more than 4% of the total source flux within the 1.7–3.0 keV band, and places an upper limit on the charge exchange interaction velocity at 450 km s$^{-1}$. This result supports ongoing shock–cloud interactions within N 132D and highlights the unique capabilities of XRISM to probe the complex physical processes at play.
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Publications of the Astronomical Society of Japan, 77(Supplement_1) S1-S9, Apr 11, 2025Abstract The X-Ray Imaging and Spectroscopy Mission (XRISM) is a joint mission between the Japan Aerospace Exploration Agency (JAXA) and the National Aeronautics and Space Administration (NASA) in collaboration with the European Space Agency (ESA). In addition to the three space agencies, universities and research institutes from Japan, North America, and Europe have joined to contribute to developing satellite and onboard instruments, data-processing software, and the scientific observation program. XRISM is the successor to the ASTRO-H (Hitomi) mission, which ended prematurely in 2016. Its primary science goal is to examine astrophysical problems with precise, high-resolution X-ray spectroscopy. XRISM promises to discover new horizons in X-ray astronomy. It carries a 6 × 6 pixelized X-ray microcalorimeter on the focal plane of an X-ray mirror assembly (Resolve) and a co-aligned X-ray CCD camera (Xtend) that covers the same energy band over a large field of view. XRISM utilizes the Hitomi heritage, but all designs were reviewed. The attitude and orbit control system was improved in hardware and software. The spacecraft was launched from the JAXA Tanegashima Space Center on 2023 September 6 (UTC). During the in-orbit commissioning phase, the onboard components were activated. Although the gate valve protecting the Resolve sensor with a thin beryllium X-ray entrance window was not yet opened, scientific observation started in 2024 February with the planned performance verification observation program. The nominal observation program commenced with the following guest observation program beginning in 2024 September.
Misc.
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NASA/GSFC press release, Apr, 2015
Books and Other Publications
1Presentations
49-
2nd Plasma Astrophysics School and Workshop (PASW26), May 15, 2026 Invited
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International Conference on High Energy Density Laboratory Astrophysics (HEDLA), Apr 20, 2026 Invited
Teaching Experience
5-
物理学ゼミナール (東京大学)
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高エネルギー天文学特論 (東京大学 天文学専攻)
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Advanced Plasma Physics (The University of Tokyo)
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Advanced Space Physics and Astronomy (The University of Tokyo)
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JAXA宇宙科学技術講義 (立教大学)
Professional Memberships
2Research Projects
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所外施設利用共同研究 研究コア提案型共同研究, 核融合科学研究所, Apr, 2025 - Mar, 2028
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Grants-in-Aid for Scientific Research, Japan Society for the Promotion of Science, Apr, 2023 - Mar, 2027
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Grants-in-Aid for Scientific Research, Japan Society for the Promotion of Science, Apr, 2022 - Mar, 2026
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Grants-in-Aid for Scientific Research, Japan Society for the Promotion of Science, Apr, 2020 - Mar, 2023
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Grants-in-Aid for Scientific Research, Japan Society for the Promotion of Science, Apr, 2019 - Mar, 2022
● 指導学生の顕著な論文
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Student nameYuken OhshiroStudent affiliation東京大学Author(s), journal, volume number, pagination (year of publication)Ohshiro et al., ApJL 913, L34, 7 (2021)TitleDiscovery of a Highly Neutronized Ejecta Clump in the Type Ia Supernova Remnant 3C 397DOIhttps://doi.org/10.3847/2041-8213/abff5b
● 専任大学名
1-
Affiliation (university)東京大学（University of Tokyo)
