Curriculum Vitaes
Profile Information
- Affiliation
- Associate Professor, Institute of Space and Astronautical Science, Department of Space Astronomy and Astrophysics, Japan Aerospace Exploration Agency
- Degree
- 博士(理学)(Mar, 2004, 東京大学)
- Researcher number
- 60446599
- ORCID ID
https://orcid.org/0000-0003-0441-7404- J-GLOBAL ID
- 202001021434500706
- researchmap Member ID
- R000012970
Research Interests
6Research Areas
2Research History
2Education
3-
Apr, 1999 - Mar, 2001
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Apr, 1995 - Mar, 1999
Awards
2Papers
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Nature, 641(8065) 1132-1136, May 14, 2025 Peer-reviewed
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Publications of the Astronomical Society of Japan, Apr 11, 2025 Peer-reviewedAbstract 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.
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The Astrophysical Journal Letters, 982(1) L5-L5, Mar 12, 2025 Peer-reviewedAbstract 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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Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 170362-170362, Mar, 2025 Peer-reviewed
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Nature, 638(8050) 365-369, Feb 12, 2025 Peer-reviewed
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Publications of the Astronomical Society of Japan, 77(1) L1-L8, Dec 26, 2024 Peer-reviewedAbstract 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, Dec 11, 2024 Peer-reviewedAbstract 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, 76(6) 1186-1201, Oct 10, 2024 Peer-reviewedAbstract 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.
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The Astrophysical Journal Letters, 973(1) L25-L25, Sep, 2024 Peer-reviewedAbstract We present an analysis of the first two XRISM/Resolve spectra of the well-known Seyfert-1.5 active galactic nucleus (AGN) in NGC 4151, obtained in 2023 December. Our work focuses on the nature of the narrow Fe K α emission line at 6.4 keV, the strongest and most common X-ray line observed in AGN. The total line is found to consist of three components. Even the narrowest component of the line is resolved with evident Fe K α,1 (6.404 keV) and K α,2 (6.391 keV) contributions in a 2:1 flux ratio, fully consistent with neutral gas with negligible bulk velocity. Subject to the limitations of our models, the narrowest and intermediate-width components are consistent with emission from optically thin gas, suggesting that they arise in a disk atmosphere and/or wind. Modeling the three line components in terms of Keplerian broadening, they are readily associated with (1) the inner wall of the “torus,” (2) the innermost optical “broad-line region” (or “X-ray BLR”), and (3) a region with a radius of r ≃ 100 GM/c 2 that may signal a warp in the accretion disk. Viable alternative explanations of the broadest component include a fast-wind component and/or scattering; however, we find evidence of variability in the narrow Fe K α line complex on timescales consistent with small radii. The best-fit models are statistically superior to simple Voigt functions, but when fit with Voigt profiles the time-averaged lines are consistent with a projected velocity broadening of FWHM . Overall, the resolution and sensitivity of XRISM show that the narrow Fe K line in AGN is an effective probe of all key parts of the accretion flow, as it is currently understood. We discuss the implications of these findings for our understanding of AGN accretion, future studies with XRISM, and X-ray-based black hole mass measurements.
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Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray, 85-85, Aug 21, 2024
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Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray, 224-224, Aug 21, 2024
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Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray, 235-235, Aug 21, 2024
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Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray, 92-92, Aug 21, 2024
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Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray, 52-52, Aug 21, 2024
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Scientific Reports, 14(1), Feb 9, 2024 Peer-reviewedAbstract To detect and track structural changes in atomic nuclei, the systematic study of nuclear levels with firm spin-parity assignments is important. While linear polarization measurements have been applied to determine the electromagnetic character of gamma-ray transitions, the applicable range is strongly limited due to the low efficiency of the detection system. The multi-layer Cadmium-Telluride (CdTe) Compton camera can be a state-of-the-art gamma-ray polarimeter for nuclear spectroscopy with the high position sensitivity and the detection efficiency. We demonstrated the capability to operate this detector as a reliable gamma-ray polarimeter by using polarized 847-keV gamma rays produced by the $$^{56}\textrm{Fe}$$($${ p},{ p'}\gamma $$) reaction. By combining the experimental data and simulated calculations, the modulation curve for the gamma ray was successfully obtained. A remarkably high polarization sensitivity was achieved, compatible with a reasonable detection efficiency. Based on the obtained results, a possible future gamma-ray polarimetery is discussed.
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Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1059 169024-169024, Feb, 2024 Peer-reviewed
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Meteoritics and Planetary Science, 2024 Peer-reviewed
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IEEE Transactions on Radiation and Plasma Medical Sciences, 7(8) 860-870, Nov, 2023 Peer-reviewed
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Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1050 168175-168175, May, 2023 Peer-reviewed
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Physical Review Letters, 130(17), Apr 27, 2023 Peer-reviewed
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Physical Review Letters, 130(11), Mar 15, 2023 Peer-reviewed
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ACS Earth and Space Chemistry, 7(4) 699-711, Mar 9, 2023 Peer-reviewed
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Journal of Instrumentation, 18(01) P01030-P01030, Jan 1, 2023 Peer-reviewedAbstract We have developed a γ-ray computed tomography system using a CdTe double-sided strip detector. Owing to a 250 μm fine strip pitch and high energy resolution with photon-counting capability, the system provides highly accurate images, with which the materials and their distributions inside the target can be determined according to the photon transmittances. We evaluated the key performance of the system, conducting transmission measurements for Al, Cu, and Pb plates and also for Al, Fe, Cu, and Pb rod-phantoms, both using X-rays (∼30 keV) and γ-rays (∼80 keV) from a 133Ba source. The measured transmittances agreed well with the calculated values from simulations. We successfully reconstructed the three-dimensional structure of the rod-phantom and distinguished the elements inside the phantom. Compared with the simulated photon transmittances, we found that material identification based on tomographic images obtained with the system is efficient as long as the target object does not contain thick high-Z elements.
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Science, 379(6634), Sep 22, 2022 Peer-reviewedSamples of the carbonaceous asteroid Ryugu were brought to Earth by the Hayabusa2 spacecraft. We analyzed seventeen Ryugu samples measuring 1-8 mm. CO 2 -bearing water inclusions are present within a pyrrhotite crystal, indicating that Ryugu’s parent asteroid formed in the outer Solar System. The samples contain low abundances of materials that formed at high temperatures, such as chondrules and Ca, Al-rich inclusions. The samples are rich in phyllosilicates and carbonates, which formed by aqueous alteration reactions at low temperature, high pH, and water/rock ratios < 1 (by mass). Less altered fragments contain olivine, pyroxene, amorphous silicates, calcite, and phosphide. Numerical simulations, based on the mineralogical and physical properties of the samples, indicate Ryugu’s parent body formed ~ 2 million years after the beginning of Solar System formation.
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RADIOISOTOPES, 71(2) 141-151, Jul 15, 2022 Peer-reviewed
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IEEE Transactions on Radiation and Plasma Medical Sciences, 6(5) 592-600, May, 2022 Peer-reviewed
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Nature Biomedical Engineering, 6(5) 640-647, Apr 4, 2022 Peer-reviewed
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Scientific Reports, 12(1), Mar 28, 2022 Peer-reviewedAbstract Elemental analysis based on muonic X-rays resulting from muon irradiation provides information about bulk material composition without causing damage, which is essential in the case of precious or otherwise unreachable samples, such as in archeology and planetary science. We developed a three-dimensional (3D) elemental analysis technique by combining the elemental analysis method based on negative muons with an imaging cadmium telluride double-sided strip detector (CdTe-DSD) designed for the hard X-ray and soft $$\gamma$$-ray observation. A muon irradiation experiment using spherical plastic samples was conducted at the Japan Proton Accelerator Research Complex (J-PARC); a set of projection images was taken by the CdTe-DSD, equipped with a pinhole collimator, for different sample rotation angles. The projection images measured by the CdTe-DSD were utilized to obtain a 3D volumetric phantom by using the maximum likelihood expectation maximization algorithm. The reconstructed phantom successfully revealed the 3D distribution of carbon in the bulk samples and the stopping depth of the muons. This result demonstrated the feasibility of the proposed non-destructive 3D elemental analysis method for bulk material analysis based on muonic X-rays.
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Physical Review A, 105(2), Feb 17, 2022 Peer-reviewed
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IEEE Transactions on Nuclear Science, 68(8) 2279-2285, Aug, 2021 Peer-reviewed
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IEEE Transactions on Applied Superconductivity, 31(5), Aug, 2021 Peer-reviewed
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Deexcitation Dynamics of Muonic Atoms Revealed by High-Precision Spectroscopy of Electronic K X RaysPhysical Review Letters, 127(5), Jul 27, 2021 Peer-reviewed
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Review of Scientific Instruments, 92(6), Jun 1, 2021 Peer-reviewed
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Proceedings of SPIE - The International Society for Optical Engineering, 11821, 2021
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Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 982, Dec 1, 2020 Peer-reviewed
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Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 978, Oct 21, 2020 Peer-reviewed
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Journal of Astronomical Telescopes, Instruments, and Systems, 6(4), Oct 1, 2020 Peer-reviewed
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Journal of Low Temperature Physics, 200(5-6) 445-451, Sep 1, 2020 Peer-reviewed
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Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 954, Feb 21, 2020 Peer-reviewed
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Physics in Medicine and Biology, 65(5), 2020 Peer-reviewed
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Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 924 327-331, Apr, 2019 Peer-reviewed
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Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 924 321-326, Apr, 2019 Peer-reviewed
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Proceedings of SPIE - The International Society for Optical Engineering, 11118, 2019 Peer-reviewed
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Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 912 57-60, Dec 21, 2018 Peer-reviewed
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Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 912 199-204, Dec 21, 2018 Peer-reviewed
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Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 912 191-194, Dec 21, 2018 Peer-reviewed
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Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 912 269-273, Dec 21, 2018 Peer-reviewed
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Physics in Medicine and Biology, 63(20), Oct 16, 2018 Peer-reviewed
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Publications of the Astronomical Society of Japan, 70(6), Oct 1, 2018 Peer-reviewedCorresponding author
Misc.
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Proceedings of 38th International Cosmic Ray Conference — PoS(ICRC2023), Aug 18, 2023
Presentations
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日本天文学会2025年春季年会, Mar 19, 2025
Research Projects
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科学研究費助成事業, 日本学術振興会, Apr, 2024 - Mar, 2029
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科学研究費助成事業, 日本学術振興会, Apr, 2025 - Mar, 2028
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科学研究費助成事業 基盤研究(A), 日本学術振興会, Apr, 2021 - Mar, 2025
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科学研究費助成事業 基盤研究(A), 日本学術振興会, Apr, 2020 - Mar, 2024
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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, 2018 - Mar, 2023
