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
231-
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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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.
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The Astrophysical Journal Letters, 977(2) L34-L34, Dec 11, 2024Abstract 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, Oct 10, 2024Abstract 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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Space Telescopes and Instrumentation 2024: Optical, Infrared, and Millimeter Wave, 81-81, Sep 10, 2024
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The Astrophysical Journal Letters, 973(1) L25-L25, Sep 1, 2024Abstract 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, 228-228, Aug 21, 2024
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Cryogenics, 138 103795-103795, Mar, 2024
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Acta Astronaut., 213 29-34, Dec, 2023 Peer-reviewed
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Acta Astronaut., 202 617-624, Jan, 2023 Peer-reviewed
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Journal of Low Temperature Physics, 209(5-6) 1097-1103, Dec, 2022
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Progress of Theoretical and Experimental Physics, 2023(4), Nov 21, 2022Abstract LiteBIRD the Lite (Light) satellite for the study of B-mode polarization and Inflation from cosmic background Radiation Detection, is a space mission for primordial cosmology and fundamental physics. The Japan Aerospace Exploration Agency (JAXA) selected LiteBIRD in May 2019 as a strategic large-class (L-class) mission, with an expected launch in the late 2020s using JAXA’s H3 rocket. LiteBIRD is planned to orbit the Sun-Earth Lagrangian point L2, where it will map the cosmic microwave background (CMB) polarization over the entire sky for three years, with three telescopes in 15 frequency bands between 34 and 448 GHz, to achieve an unprecedented total sensitivity of 2.2 μK-arcmin, with a typical angular resolution of 0.5○ at 100 GHz. The primary scientific objective of LiteBIRD is to search for the signal from cosmic inflation, either making a discovery or ruling out well-motivated inflationary models. The measurements of LiteBIRD will also provide us with insight into the quantum nature of gravity and other new physics beyond the standard models of particle physics and cosmology. We provide an overview of the LiteBIRD project, including scientific objectives, mission and system requirements, operation concept, spacecraft and payload module design, expected scientific outcomes, potential design extensions and synergies with other projects. Subject Index LiteBIRD cosmic inflation, cosmic microwave background, B-mode polarization, primordial gravitational waves, quantum gravity, space telescope
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Publications of the Astronomical Society of Japan, 75(1) 30-36, Nov 12, 2022Abstract 2S 0921−630 is an eclipsing low-mass X-ray binary (LMXB) with an orbital period of ∼9 d. Past X-ray observations have revealed that 2S 0921−630 has an extended accretion disk corona (ADC), from which most of the X-rays from the system are emitted. We report the result of our Suzaku archival data analysis of 2S 0921−630. The average X-ray spectrum is reproduced with a blackbody emission (kTbb ∼ 0.3 keV) Comptonized by optically thick gas (“Compton cloud”; optical depth τ ∼ 21) with a temperature of ∼2 keV, combined with 13 emission lines. We find that most of the emission lines correspond to highly ionized atoms: O, Ne, Mg, Si, S, Ar, and Fe. A Kα emission line and an absorption edge of semi-neutral iron (Fe textsci– textscxvii) are also detected. The semi-neutral iron Kα line is significantly broad, with a width of 0.11 ± 0.02 keV in sigma, which corresponds to the Doppler broadening by the Kepler motion at a radius of ∼109 cm. We suggest that the observed semi-neutral iron line originates at the inner part of the accretion disk in the immediate outside of the Compton cloud, i.e., the Compton cloud may have a radius of ∼109 cm.
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JOURNAL OF LOW TEMPERATURE PHYSICS, Nov, 2022
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Journal of Low Temperature Physics, 209(3-4) 396-408, Sep 5, 2022
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Space Telescopes and Instrumentation 2022: Optical, Infrared, and Millimeter Wave, Aug 27, 2022
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SPACE TELESCOPES AND INSTRUMENTATION 2022: OPTICAL, INFRARED, AND MILLIMETER WAVE, 12180, 2022
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Publications of the Astronomical Society of Japan, 73(2) 286-301, Apr 5, 2021 Peer-reviewed<title>Abstract</title> Pulse-phase-resolved X-ray spectra of the X-ray pulsar Her X-1 observed with Suzaku are analyzed. The analysis is based on a hypothesis that the observed variations of the continuum spectra associated with the neutron star spin originate in the changes of the projection areas of the emission regions viewed from the observer, and that the spectral shape observed from each of the emission regions does not change with the viewing angle variation. We calculate the ratios of the fluxes in each energy bin between arbitrary pairs of the pulse-phase-resolved spectra over the entire energy range. We identify flat portions in these ratio spectra, which are likely to indicate the intrinsic emission components that have invariant spectral shapes, in the three energy bands of below ∼1 keV, 2–6 keV, and above ∼18 keV. Then, we approximately solve the simultaneous equations for the intrinsic spectral components from a pair of the phase-resolved spectra that show flat portions in the ratio spectrum. As a result, spectra of the three components are obtained as the low-, medium-, and high-energy bands corresponding to those for the flat portions. They are found to be well fitted with a soft blackbody, a cut-off power law, and a hard blackbody model, respectively. Finally, we fit all the phase-resolved spectra simultaneously with a composite model of three continuum components together with a cyclotron absorption feature and an iron line, and obtain an acceptable result. The origins of the cut-off power-law and hard blackbody components are discussed in relation to recently developed theoretical models.
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Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 984 164646-164646, Dec, 2020 Peer-reviewed
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Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 978 164374-164374, Oct, 2020 Peer-reviewed
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Journal of Low Temperature Physics, 199(3-4) 1107-1117, May, 2020 Peer-reviewed
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Proceedings of SPIE - The International Society for Optical Engineering, 11444, 2020
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Journal of Astronomical Telescopes, Instruments, and Systems, 5(4), Oct 1, 2019 Peer-reviewed
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J INSTRUM, 14(4) C04003, Apr, 2019 Peer-reviewed
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Journal of Low Temperature Physics, 194(5-6) 443-452, Mar 15, 2019 Peer-reviewed
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Journal of Low Temperature Physics, 193(5-6) 1048-1056, Dec 1, 2018 Peer-reviewed
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Publications of the Astronomical Society of Japan, 70(6) 113, Oct 1, 2018 Peer-reviewed
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JOURNAL OF ASTRONOMICAL TELESCOPES INSTRUMENTS AND SYSTEMS, 4(2), Apr, 2018
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Publications of the Astronomical Society of Japan, 70(2), Mar 1, 2018
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Publications of the Astronomical Society of Japan, 70(2), Mar 1, 2018
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Publications of the Astronomical Society of Japan, 70(2), Mar 1, 2018
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN, 70(2), Mar, 2018
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Publications of the Astronomical Society of Japan, 70(2) 13, Mar, 2018 Peer-reviewedThe origin of the narrow Fe-K{\alpha} fluorescence line at 6.4 keV from<br /> active galactic nuclei has long been under debate; some of the possible sites<br /> are the outer accretion disk, the broad line region, a molecular torus, or<br /> interstellar/intracluster media. In February-March 2016, we performed the first<br /> X-ray microcalorimeter spectroscopy with the Soft X-ray Spectrometer (SXS)<br /> onboard the Hitomi satellite of the Fanaroff-Riley type I radio galaxy NGC 1275<br /> at the center of the Perseus cluster of galaxies. With the high energy<br /> resolution of ~5 eV at 6 keV achieved by Hitomi/SXS, we detected the<br /> Fe-K{\alpha} line with ~5.4 {\sigma} significance. The velocity width is<br /> constrained to be 500-1600 km s$^{-1}$ (FWHM for Gaussian models) at 90%<br /> confidence. The SXS also constrains the continuum level from the NGC 1275<br /> nucleus up to ~20 keV, giving an equivalent width ~20 eV of the 6.4 keV line.<br /> Because the velocity width is narrower than that of broad H{\alpha} line of<br /> ~2750 km s$^{-1}$, we can exclude a large contribution to the line flux from<br /> the accretion disk and the broad line region. Furthermore, we performed pixel<br /> map analyses on the Hitomi/SXS data and image analyses on the Chandra archival<br /> data, and revealed that the Fe-K{\alpha} line comes from a region within ~1.6<br /> kpc from the NGC 1275 core, where an active galactic nucleus emission<br /> dominates, rather than that from intracluster media. Therefore, we suggest that<br /> the source of the Fe-K{\alpha} line from NGC 1275 is likely a low-covering<br /> fraction molecular torus or a rotating molecular disk which probably extends<br /> from a pc to hundreds pc scale in the active galactic nucleus system.
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Publications of the Astronomical Society of Japan, 70(3) 38, Feb 14, 2018 Peer-reviewedWe present results from the Hitomi X-ray observation of a young<br /> composite-type supernova remnant (SNR) G21.5$-$0.9, whose emission is dominated<br /> by the pulsar wind nebula (PWN) contribution. The X-ray spectra in the 0.8-80<br /> keV range obtained with the Soft X-ray Spectrometer (SXS), Soft X-ray Imager<br /> (SXI) and Hard X-ray Imager (HXI) show a significant break in the continuum as<br /> previously found with the NuSTAR observation. After taking into account all<br /> known emissions from the SNR other than the PWN itself, we find that the Hitomi<br /> spectra can be fitted with a broken power law with photon indices of<br /> $\Gamma_1=1.74\pm0.02$ and $\Gamma_2=2.14\pm0.01$ below and above the break at<br /> $7.1\pm0.3$ keV, which is significantly lower than the NuSTAR result ($\sim9.0$<br /> keV). The spectral break cannot be reproduced by time-dependent particle<br /> injection one-zone spectral energy distribution models, which strongly<br /> indicates that a more complex emission model is needed, as suggested by recent<br /> theoretical models. We also search for narrow emission or absorption lines with<br /> the SXS, and perform a timing analysis of PSR J1833$-$1034 with the HXI and<br /> SGD. No significant pulsation is found from the pulsar. However, unexpectedly,<br /> narrow absorption line features are detected in the SXS data at 4.2345 keV and<br /> 9.296 keV with a significance of 3.65 $\sigma$. While the origin of these<br /> features is not understood, their mere detection opens up a new field of<br /> research and was only possible with the high resolution, sensitivity and<br /> ability to measure extended sources provided by an X-ray microcalorimeter.
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Proceedings of SPIE - The International Society for Optical Engineering, 10698, 2018
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Proceedings of SPIE - The International Society for Optical Engineering, 10698, 2018
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SPACE TELESCOPES AND INSTRUMENTATION 2018: OPTICAL, INFRARED, AND MILLIMETER WAVE, 10698, 2018
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SPACE TELESCOPES AND INSTRUMENTATION 2018: OPTICAL, INFRARED, AND MILLIMETER WAVE, 10698, 2018
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Publications of the Astronomical Society of Japan, 70(2) 16, 2018 Peer-reviewed
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Journal of Low Temperature Physics, 193(5-6) 841-850, 2018 Peer-reviewed
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Publications of the Astronomical Society of Japan, 70(2), 2018 Peer-reviewed
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Publications of the Astronomical Society of Japan, 70(2), 2018 Peer-reviewed
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Journal of Astronomical Telescopes, Instruments, and Systems, 4(1), 2018 Peer-reviewed
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NATURE, 551(7681) 478-+, Nov, 2017 Peer-reviewed
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN, 69(4), Aug, 2017 Peer-reviewed
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ASTROPHYSICAL JOURNAL, 837(1), Mar, 2017 Peer-reviewed
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN, 68(SP1) id. S15, Jun, 2016 Peer-reviewed
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Meeting Abstracts of the Physical Society of Japan, 71 510-510, 2016
Misc.
201Professional 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)
