宇宙物理学研究系
Profile Information
- Affiliation
- Professor, Institute of Space and Astronautical Science, Department of Astrophysics, Japan Aerospace Exploration Agency
- J-GLOBAL ID
- 201801002962836691
- researchmap Member ID
- B000323419
- External link
Research Interests
2Research Areas
1Research History
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Aug, 2005 - Present
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Apr, 1992 - Jul, 2005
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Aug, 2001 - Dec, 2004
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Apr, 1991 - Mar, 1992
Education
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Apr, 1986 - Mar, 1991
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Apr, 1980 - Mar, 1986
Committee Memberships
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Nov, 2020 - Present
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Apr, 2020 - Present
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Apr, 2020 - Present
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Apr, 2020 - Present
Papers
258-
Publications of the Astronomical Society of Japan, Oct 7, 2025
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The Astrophysical Journal Letters, 982(1) L5-L5, Mar 12, 2025Abstract 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, Feb 12, 2025
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International Journal of Modern Physics A, Jan 29, 2025Recent direct measurements of the energy spectra of the charged cosmic ray have revealed unexpected spectral features, most notably the onset of a progressive hardening at few hundreds of GeV/n not only of proton and He spectra but also observable for heavier nuclei. Thus, the study of the spectra behavior of heavy elements may shed light on understanding propagation and acceleration phenomena in our Galaxy. In particular, Fe and Ni provide favorable conditions for observations thanks to the low background contamination from spallation of higher mass elements they are affected by. The CALorimetric Electron Telescope, CALET, has been measuring high-energy cosmic rays on the International Space Station since October 2015. The instrument consists of two layers of segmented plastic scintillators, a 3 radiation length thick tungsten-scintillating fiber imaging calorimeter and a 27 radiation length thick PWO calorimeter. It identifies the charge of individual elements up to Ni and beyond and it measures the energy of cosmic-ray nuclei providing a direct measurement of their spectra. In this contribution, the iron and nickel spectra, resulted after 5 years of data acquisition, are presented in the energy range between 10 and 2000 GeV/n and between 8.8 and 240 GeV/n, respectively. The analysis procedure and the assessment of systematic errors are detailed, in addition to the ratio between the two fluxes. Both spectra show similar shape and energy dependence.
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Publications of the Astronomical Society of Japan, Dec 26, 2024Abstract 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.
Misc.
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ASTRONOMICAL DATA ANALYSIS SOFTWARE AND SYSTEMS XXVI, 521 205-208, 2019
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ASTRONOMICAL DATA ANALYSIS SOFTWARE AND SYSTEMS XXVIII, 523 515-518, 2019
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ASTRONOMICAL DATA ANALYSIS SOFTWARE AND SYSTEMS XXVI, 521 46-49, 2019
Presentations
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第1回 SPARC Japan セミナー2020 「研究データ公開：フルオープンと制限公開の境界線」, Oct 2, 2020 Invited
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JpGU-AGU Joint Meeting 2020:Virtual ユニオンセッション U-12 「地球惑星科学の進むべき道10 ビッグデータとオープンサイエンス」, Jul 15, 2020 Invited
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20 Years of Chandra Science Symposium
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The 29th annual international Astronomical Data Analysis Software & Systems (ADASS)
Professional Memberships
1Research Projects
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科学研究費助成事業, 日本学術振興会, Apr, 2024 - Mar, 2027
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Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C), Japan Society for the Promotion of Science, Apr, 2016 - Mar, 2019
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Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C), Japan Society for the Promotion of Science, 2009 - 2011
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Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B), Japan Society for the Promotion of Science, 2007 - 2009
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Grants-in-Aid for Scientific Research Grant-in-Aid for international Scientific Research, Japan Society for the Promotion of Science, 1992 - 1994
