Curriculum Vitaes
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
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Apr, 2003 - Mar, 2008
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Apr, 1999 - Mar, 2003
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Apr, 1996 - Mar, 1999
Committee Memberships
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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
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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.
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The Astrophysical Journal, 982(2) 190-190, Mar 28, 2025Abstract Measuring shock velocities is crucial for understanding the energy transfer processes at the shock fronts of supernova remnants (SNRs), including acceleration of cosmic rays. Here we present shock velocity measurements on the SNR N132D, based on the thermal properties of the shock-heated interstellar medium. We apply a self-consistent model developed in our previous work to X-ray data from deep Chandra observations with an effective exposure of ∼900 ks. In our model, both temperature and ionization relaxation processes in postshock plasmas are simultaneously calculated, so that we can trace back to the initial condition of the shock-heated plasma to constrain the shock velocity. We reveal that the shock velocity ranges from 800 to 1500 km s−1 with moderate azimuthal dependence. Although our measurement is consistent with the velocity determined by independent proper motion measurements in the south rim regions, a large discrepancy between the two measurements (up to a factor of 4) is found in the north rim regions. This implies that a substantial amount of the kinetic energy has been transferred to the nonthermal component through highly efficient particle acceleration. Our results are qualitatively consistent with the gamma-ray observations of this SNR.
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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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Publications of the Astronomical Society of Japan, 77(1) L1-L8, 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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The Astrophysical Journal, 976(2) 180-180, Nov 21, 2024Abstract X-ray observations of shock-heated plasmas, such as those found in supernova remnants (SNRs), often exhibit features of temperature and ionization nonequilibrium. For accurate interpretation of these observations, proper calculations of the equilibration processes are essential. Here, we present a self-consistent model of thermal X-ray emission from shock-heated plasmas that accounts for both temperature and ionization nonequilibrium conditions. For a given pair of shock velocity and initial electron-to-ion temperature ratio, the temporal evolution of the temperature and ionization state of each element was calculated by simultaneously solving the relaxation processes of temperature and ionization. The resulting thermal X-ray spectrum was synthesized by combining our model with the AtomDB spectral code. Comparison between our model and the nei model, a constant-temperature nonequilibrium ionization model available in the XSPEC software package, reveals a 30% underestimation of the ionization timescale in the nei model. We implemented our model in XSPEC to directly constrain the shock wave’s properties, such as the shock velocity and collisionless electron heating efficiency, from the thermal X-ray emission from postshock plasmas. We applied this model to archival Chandra data of the SNR N132D, providing a constraint on the shock velocity of ∼800 km s−1, in agreement with previous optical studies.
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Publications of the Astronomical Society of Japan, 76(6) 1186-1201, Oct 10, 2024 Corresponding authorAbstract 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 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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Monthly Notices of the Royal Astronomical Society, 532(1) 1087-1098, Jun 22, 2024ABSTRACT Suzaku X-ray observations of the Type Ia supernova remnant (SNR) 3C 397 discovered exceptionally high mass ratios of Mn/Fe, Ni/Fe, and Cr/Fe, consistent with a near MCh progenitor white dwarf (WD). The Suzaku observations have established 3C 397 as our best candidate for a near-MCh SNR Ia, and opened the way to address additional outstanding questions about the origin and explosion mechanism of these transients. In particular, subsequent XMM–Newton observations revealed an unusually clumpy distribution of iron group elemental (IGE) abundances within the ejecta of 3C 397. In this paper, we undertake a suite of two-dimensional hydrodynamical models, varying both the explosion mechanism – either deflagration-to-detonation (DDT), or pure deflagration – WD progenitors, and WD progenitor metallicity, and analyse their detailed nucleosynthetic abundances and associated clumping. We find that pure deflagrations naturally give rise to clumpy distributions of neutronized species concentrated towards the outer limb of the remnant and confirm DDTs have smoothly structured ejecta with a central concentration of neutronization. Our findings indicate that 3C 397 was most likely a pure deflagration of a high central density WD. We discuss a range of implications of these findings for the broader SN Ia progenitor problem.
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The Astrophysical Journal, 968(2) 95-95, Jun 1, 2024Abstract The discovery of coherent pulsations from several ultraluminous X-ray pulsars (ULXPs) has provided direct evidence of a supercritical accretion flow. However, the geometrical structure of such an accretion flow onto the central neutron star remains poorly understood. NGC 5907 ULX1 is one of the most luminous ULXPs, with a luminosity exceeding 1041 erg s−1. Here we present a broadband X-ray study of this ULXP using the data from simultaneous observations with XMM-Newton and NuSTAR conducted in 2014 July. The phase-resolved spectra are well reproduced by a model consisting of a multicolor disk blackbody emission with a temperature gradient of p = 0.5 (T ∝ r −p ) and a power law with an exponential cutoff. The disk component is phase-invariant and has an innermost temperature of ∼ 0.3 keV. Its normalization suggests a relatively low inclination angle of the disk, in contrast to the previous claims in other literature. The power-law component, attributed to the emission from the accretion flow inside the magnetosphere of the neutron star, indicates phase-dependent spectral shape changes; the spectrum is slightly harder in the pre-peak phase than in the post-peak phase. This implies that the magnetosphere has an asymmetric geometry around the magnetic axis and that hotter regions close to the magnetic pole become visible before the pulse peak.
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Plasma and Fusion Research, 18 2401041-2401041, Jun 22, 2023
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The Astrophysical Journal, 940(2) 105-105, Nov 25, 2022Abstract Mechanisms of particle heating are crucial to understanding the shock physics in supernova remnants (SNRs). However, there has been little information on time variabilities of thermalized particles so far. Here, we present a discovery of a gradually brightening thermal X-ray emission found in the Chandra data of Tycho’s SNR obtained during 2000–2015. The emission exhibits a knot-like feature (Knot1) with a diameter of ≃0.04 pc located in the northwestern limb, where we also find localized Hα filaments in an optical image taken with the Hubble Space Telescope in 2008. The model with the solar abundance reproduces the spectra of Knot1, suggesting that Knot1 originates from the interstellar medium; this is the first detection of thermal X-ray emission from swept-up gas found in Tycho’s SNR. Our spectral analysis indicates that the electron temperature of Knot1 has increased from ∼0.30 to ∼0.69 keV within the period between 2000 and 2015. These results lead us to ascribe the time-variable emission to a small dense clump recently heated by the forward shock at the location of Knot1. The electron-to-proton temperature ratio immediately downstream of the shock (β 0 ≡ T e /T p ) is constrained to be m e /m p ≤ β 0 ≤ 0.15 to reproduce the data, indicating the collisionless electron heating with efficiency is consistent with previous Hα observations of Tycho and other SNRs with high shock velocities.
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The Astrophysical Journal, 938(1) 52-52, Oct 1, 2022Abstract It is generally believed that Type Ia supernovae are thermonuclear explosions of carbon–oxygen white dwarfs (WDs). However, there is currently no consensus regarding the events leading to the explosion. A binary WD (WD–WD) merger is a possible progenitor of Type Ia supernovae. Space-based gravitational wave (GW) detectors with considerable sensitivity in the decihertz range such as the DECi-hertz Interferometer Gravitational wave Observatory (DECIGO) can observe WD–WD mergers directly. Therefore, access to the decihertz band of GWs would enable multi-messenger observations of Type Ia supernovae to determine their progenitors and explosion mechanism. In this paper, we consider the event rate of WD–WD mergers and the minimum detection range to observe one WD–WD merger per year, using a nearby galaxy catalog and the relation between Ia supernovae and their host galaxies. Furthermore, we calculate DECIGO’s ability to localize WD–WD mergers and to determine the masses of binary mergers. We estimate that a decihertz GW observatory can detect GWs with amplitudes of h ∼ 10−20 [Hz−1/2] at 0.01–0.1 Hz, which is 1000 times higher than the detection limit of DECIGO. Assuming the progenitors of Ia supernovae are merging WD–WD (1 M⊙ and 0.8 M⊙), DECIGO is expected to detect 6600 WD–WD mergers within z = 0.08, and identify the host galaxies of such WD–WD mergers within z ∼ 0.065 using GW detections alone.
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The Astrophysical Journal, 933(2) 157-157, Jul 1, 2022Abstract We report new H i observations of the Type Ia supernova remnant (SNR) SN 1006 using the Australia Telescope Compact Array with an angular resolution of $4\buildrel{\,\prime}\over{.} 5\times 1\buildrel{\,\prime}\over{.} 4$ (∼2 pc at the assumed SNR distance of 2.2 kpc). We find an expanding gas motion in position–velocity diagrams of H i with an expansion velocity of ∼4 km s−1 and a mass of ∼1000 M⊙. The spatial extent of the expanding shell is roughly the same as that of SN 1006. We here propose a hypothesis that SN 1006 exploded inside the wind-blown bubble formed by accretion winds from the progenitor system consisting of a white dwarf and a companion star, and then the forward shock has already reached the wind wall. This scenario is consistent with the single-degenerate model. We also derived the total energy of cosmic-ray protons Wp to be only ∼1.2–2.0 × 1047 erg by adopting the averaged interstellar proton density of ∼25 cm−3. The small value is compatible with the relation between the age and Wp of other gamma-ray SNRs with ages below ∼6 kyr. The Wp value in SN 1006 will possibly increase up to several 1049 erg in the next ∼5 kyr via the cosmic-ray diffusion into the H i wind shell.
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Publications of the Astronomical Society of Japan, 73(5) 1405-1417, Oct 4, 2021 Peer-reviewedAbstract We discover an unidentified strong emission feature in the X-ray spectrum of EXO 1745−248 obtained by RXTE at 40 hr after the peak of a superburst. The structure was centered at 6.6 keV and significantly broadened with a large equivalent width of 4.3 keV, corresponding to a line photon flux of 4.7 × 10−3 ph cm−2 s−1. The 3–20 keV spectrum was reproduced successfully by a power-law continuum with narrow and broad (2.7 keV in full width at half maximum) Gaussian emission components. Alternatively, the feature can be described by four narrow Gaussians, centered at 5.5 keV, 6.5 keV, 7.5 keV, and 8.6 keV. Considering the strength and shape of the feature, it is unlikely to have originated from reflection of the continuum X-rays by some optically thick material, such as an accretion disk. Moreover, the intensity of the emission structure decreased significantly with an exponential time scale of 1 hr. The feature was not detected in an INTEGRAL observation performed 10 hr before the RXTE observation with a line flux upper limit of 1.5 × 10−3 ph cm−2 s−1. The observed emission structure is consistent with gravitationally redshifted charge exchange emission from Ti, Cr, Fe, and Co. We suggest that the emission results from a charge exchange interaction between a highly metal-enriched fall-back ionized burst wind and an accretion disk, at a distance of ∼60 km from the neutron star. If this interpretation is correct, the results provide new information on nuclear burning processes during thermonuclear X-ray bursts.
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The Astrophysical Journal Letters, 913(2) L34-L34, Jun 1, 2021 Peer-reviewedAbstract The supernova remnant (SNR) 3C 397 is thought to originate from a Type Ia supernova (SN Ia) explosion of a near-Chandrasekhar-mass (MCh) progenitor, based on the enhanced abundances of Mn and Ni revealed by previous X-ray study with Suzaku. Here we report follow-up XMM-Newton observations of this SNR, conducted with the aim of investigating the detailed spatial distribution of the Fe-peak elements. We have discovered an ejecta clump with extremely high abundances of Ti and Cr, in addition to Mn, Fe, and Ni, in the southern part of the SNR. The Fe mass of this ejecta clump is estimated to be ∼0.06 M⊙, under the assumption of a typical Fe yield for SNe Ia (i.e., ∼0.8 M⊙). The observed mass ratios among the Fe-peak elements and Ti require substantial neutronization that is achieved only in the innermost regions of a near-MCh SN Ia with a central density of ρc ∼ 5 × 109 g cm−3, significantly higher than typically assumed for standard near-MCh SNe Ia (ρc ∼ 2 × 109 g cm−3). The overproduction of the neutron-rich isotopes (e.g., 50Ti and 54Cr) is significant in such high-ρc SNe Ia, with respect to the solar composition. Therefore, if 3C 397 is a typical high-ρc near-MCh SN Ia remnant, the solar abundances of these isotopes could be reproduced by the mixture of the high- and low-ρc near-MCh and sub-MCh Type Ia events, with ≲20% being high-ρc near-MCh.
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The Astrophysical Journal Letters, 910(2) L24-L24, Apr 1, 2021 Peer-reviewedLead authorAbstract The geometric structure of supernova remnants (SNR) provides a clue to unveiling the pre-explosion evolution of their progenitors. Here we present an X-ray study of N103B (0509–68.7), a Type Ia SNR in the Large Magellanic Cloud, that is known to be interacting with dense circumstellar matter (CSM). Applying our novel method for feature extraction to deep Chandra observations, we have successfully resolved the CSM, Fe-rich ejecta, and intermediate-mass element (IME) ejecta components, and revealed each of their spatial distributions. Remarkably, the IME ejecta component exhibits a double-ring structure, implying that the SNR expands into an hourglass-shape cavity and thus forms bipolar bubbles of the ejecta. This interpretation is supported by more quantitative spectroscopy that reveals a clear bimodality in the distribution of the ionization state of the IME ejecta. These observational results can be naturally explained if the progenitor binary system had formed a dense CSM torus on the orbital plane prior to the explosion, providing further evidence that the SNR N103B originates from a single-degenerate progenitor.
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The Astrophysical Journal Letters, 906 L3, Jan, 2021 Peer-reviewed
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The Astrophysical Journal (in press), Jul, 2020 Peer-reviewed
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The Astrophysical Journal, 897(1) 62, Jul, 2020 Peer-reviewed
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The Astrophysical Journal, 890(1) 62, Feb, 2020 Peer-reviewed
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Astronomische Nachrichten, 341(2) 150-155, Feb, 2020 Peer-reviewedInvitedLead author
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Monthly Notices of the Royal Astronomical Society, 483(2) 1701-1721, Feb, 2019 Peer-reviewed
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Space Science Reviews, 214(8) 129, Dec, 2018 Peer-reviewedInvited
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The Astrophysical Journal Letters, 868 L35, Dec, 2018 Peer-reviewedLead author
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The Astrophysical Journal, 867(1) 7, Nov, 2018 Peer-reviewed
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The Astrophysical Journal, 865(2) 151, Oct, 2018 Peer-reviewed
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The Astrophysical Journal Letters, 866(2) L26, Oct, 2018 Peer-reviewed
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Publications of the Astronomical Society of Japan, 70(5) 88, Oct, 2018 Peer-reviewed
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Space Science Reviews, 214(7) 108, Oct, 2018 Peer-reviewedInvited
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Publications of the Astronomical Society of Japan, 70(2) 16, Mar, 2018 Peer-reviewedCorresponding author
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NATURE, 551(7681) 478-+, Nov, 2017 Peer-reviewedCorresponding author
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The Astrophysical Journal, 846(1) 77, Sep, 2017 Peer-reviewed
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The Astrophysical Journal, 843(1) 35, Jul, 2017 Peer-reviewed
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The Astrophysical Journal, 842(1) 28, Jun, 2017 Peer-reviewed
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ASTROPHYSICAL JOURNAL, 834(2) 124, Jan, 2017 Peer-reviewed
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Nature, 535(7610) 117, Jul, 2016 Peer-reviewed
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The Astrophysical Journal Letters, 820(1) L3, Mar, 2016 Peer-reviewed
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The Astrophysical Journal, 808(1) 77, Jul, 2015 Peer-reviewed
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The Astrophysical Journal, 801(2) 92, Mar, 2015 Peer-reviewed
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The Astrophysical Journal Letters, 801(2) L31, Mar, 2015 Peer-reviewed
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ASTROPHYSICAL JOURNAL LETTERS, 785(2) L27, Apr, 2014 Peer-reviewed
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ASTROPHYSICAL JOURNAL, 780(2) 136, Jan, 2014 Peer-reviewed
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The Astrophysical Journal, 779(1) 49, Dec, 2013 Peer-reviewed
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The Astrophysical Journal, 777(2) 145, Nov, 2013 Peer-reviewed
Misc.
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NASA/GSFC press release, Apr, 2015
Books and Other Publications
1Presentations
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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
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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
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Affiliation (university)東京大学（University of Tokyo)
