研究者業績
基本情報
- 所属
- 国立研究開発法人宇宙航空研究開発機構 宇宙科学研究所 特任助教
- ORCID ID
https://orcid.org/0000-0002-7962-4136- J-GLOBAL ID
- 202501003078234700
- researchmap会員ID
- R000092664
論文
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The Astrophysical Journal 2025年8月W49B is a unique Galactic supernova remnant with centrally peaked, "bar"-like ejecta distribution, which was once considered evidence for a hypernova origin that resulted in a bipolar ejection of the stellar core. However, chemical abundance measurements contradict this interpretation. Closely connected to the morphology of the ejecta is its velocity distribution, which provides critical details for understanding the explosion mechanism. We report the first ever observational constraint on the kinematics of the ejecta in W49B using the Resolve microcalorimeter spectrometer on the X-ray Imaging and Spectroscopy Mission (XRISM). Using XRISM/Resolve, we measured the line-of-sight velocity traced by the Fe Heα emission, which is the brightest feature in the Resolve spectrum, to vary by ±300 km s‑1 with a smooth east-to-west gradient of a few tens of kilometers per second per parsec along the major axis. Similar trends in the line-of-sight velocity structure were found for other Fe-group elements Cr and Mn, traced by the Heα emission, and also for intermediate-mass elements Si, S, Ar, and Ca, traced by the Lyα emission. The discovery of the east–west gradient in the line-of-sight velocity, together with the absence of a twin-peaked line profile or enhanced broadening in the central region, clearly rejects the equatorially expanding disk model. In contrast, the observed velocity structure suggests bipolar flows reminiscent of a bipolar explosion scenario. An alternative scenario would be a collimation of the ejecta by an elongated cavity sculpted by bipolar stellar winds....
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Monthly Notices of the Royal Astronomical Society 2025年6月We report measurements of the linear polarization degree (PD) and angle (PA) for hard X-ray emission from the Crab pulsar and wind nebula. Measurements were made with the XL-Calibur (<inline-formula><tex-math id="TM0001" notation="LaTeX">$\sim$</tex-math></inline-formula>15-80 keV) balloon-borne Compton-scattering polarimeter in July 2024. The polarization parameters are determined using a Bayesian analysis of Stokes parameters obtained from X-ray scattering angles. Well-constrained (<inline-formula><tex-math id="TM0002" notation="LaTeX">$\sim 8.5\sigma$</tex-math></inline-formula>) results are obtained for the polarization of the <inline-formula><tex-math id="TM0003" notation="LaTeX">$\sim$</tex-math></inline-formula>19-64 keV signal integrated over all pulsar phases: PD = (25.1<inline-formula><tex-math id="TM0004" notation="LaTeX">$\pm$</tex-math></inline-formula>2.9) per cent and PA = (129.8<inline-formula><tex-math id="TM0005" notation="LaTeX">$\pm 3.2)^\circ$</tex-math></inline-formula>. In the off-pulse (nebula-dominated) phase range, the PD is constrained at <inline-formula><tex-math id="TM0006" notation="LaTeX">$\sim 4.5\sigma$</tex-math></inline-formula> and is compatible with the phase-integrated result. The PA of the nebular hard X-ray emission aligns with that measured by IXPE in the 2-8 keV band for the toroidal inner region of the pulsar wind nebula, where the hard X-rays predominantly originate. For the main pulsar peak, PD = (32.8<inline-formula><tex-math id="TM0007" notation="LaTeX">$^{+18.2}_{-28.5}$</tex-math></inline-formula>) per cent and PA = (156.0 <inline-formula><tex-math id="TM0008" notation="LaTeX">$\pm$</tex-math></inline-formula> 21.7)<inline-formula><tex-math id="TM0009" notation="LaTeX">$^\circ$</tex-math></inline-formula>, while for the second peak (inter-pulse), PD = (0.0<inline-formula><tex-math id="TM0010" notation="LaTeX">$^{+33.6}_{-0.0}$</tex-math></inline-formula>) per cent and PA = (154.5 <inline-formula><tex-math id="TM0011" notation="LaTeX">$\pm$</tex-math></inline-formula> 34.5)<inline-formula><tex-math id="TM0012" notation="LaTeX">$^\circ$</tex-math></inline-formula>. A low level of polarization in the pulsar peaks likely does not favour emission originating from the inner regions of the pulsar magnetosphere. Discriminating between Crab pulsar emission models will require deeper observations, e.g. with a satellite-borne hard X-ray polarimeter....
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The Astrophysical Journal 2025年5月20日
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Nature 2025年5月Evidence indicates that supermassive black holes (SMBHs) exist at the centres of most galaxies. Their mass correlates with the galactic bulge mass1, suggesting a coevolution with their host galaxies2, most likely through powerful winds3. X-ray observations have detected highly ionized winds outflowing at sub-relativistic speeds from the accretion disks around SMBHs4,5. However, the limited spectral resolution of present X-ray instruments has left the physical structure and location of the winds poorly understood, hindering accurate estimates of their kinetic power6,7. Here the first X-Ray Imaging and Spectroscopy Mission (XRISM) observation of the luminous quasar PDS 456 is reported. The high-resolution spectrometer Resolve aboard XRISM enabled the discovery of five discrete velocity components outflowing at 20–30% of the speed of light. This demonstrates that the wind structure is highly inhomogeneous, which probably consists of up to a million clumps. The mass outflow rate is estimated to be 60–300 solar masses per year, with the wind kinetic power exceeding the Eddington luminosity limit. Compared with the galaxy-scale outflows, the kinetic power is more than three orders of magnitude larger, whereas the momentum flux is ten times larger. These estimates disfavour both energy-driven and momentum-driven outflow models. This suggests that such wind activity occurs in less than 10% of the quasar phase and/or that its energy/momentum is not efficiently transferred to the galaxy-scale outflows owing to the clumpiness of the wind and the interstellar medium....
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The Astrophysical Journal 2025年5月The XRISM Resolve microcalorimeter array measured the velocities of hot intracluster gas at two positions in the Coma galaxy cluster: <inline-formula> <mml:math><mml:msup><mml:mrow><mml:mn>3</mml:mn></mml:mrow><mml:mrow><mml:mi>'</mml:mi></mml:mrow></mml:msup><mml:mo>×</mml:mo><mml:msup><mml:mrow><mml:mn>3</mml:mn></mml:mrow><mml:mrow><mml:mi>'</mml:mi></mml:mrow></mml:msup></mml:math> </inline-formula> squares at the center and at 6<inline-formula> <mml:math><mml:mi>'</mml:mi></mml:math> </inline-formula> (170 kpc) to the south. We find the line-of-sight velocity dispersions in those regions to be σz = 208 ± 12 km s‑1 and 202 ± 24 km s‑1, respectively. The central value corresponds to a 3D Mach number of M = 0.24 ± 0.015 and a ratio of the kinetic pressure of small-scale motions to thermal pressure in the intracluster plasma of only 3.1% ± 0.4%, at the lower end of predictions from cosmological simulations for merging clusters like Coma, and similar to that observed in the cool core of the relaxed cluster A2029. Meanwhile, the gas in both regions exhibits high line-of-sight velocity differences from the mean velocity of the cluster galaxies, Δvz = 450 ± 15 km s‑1 and 730 ± 30 km s‑1, respectively. A small contribution from an additional gas velocity component, consistent with the cluster optical mean, is detected along a sight line near the cluster center. The combination of the observed velocity dispersions and bulk velocities is not described by a Kolmogorov velocity power spectrum of steady-state turbulence; instead, the data imply a much steeper effective slope (i.e., relatively more power at larger linear scales). This may indicate either a very large dissipation scale, resulting in the suppression of small-scale motions, or a transient dynamic state of the cluster, where large-scale gas flows generated by an ongoing merger have not yet cascaded down to small scales....
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Publications of the Astronomical Society of Japan 2025年4月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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Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 2025年4月
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The Astrophysical Journal 2025年3月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 ∣vbulk∣ < 100 km s‑1. We robustly measure the field-integrated ICM velocity dispersion to be σv = 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 <inline-formula> </inline-formula> 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 2025年2月Galaxy clusters contain vast amounts of hot ionized gas known as the intracluster medium (ICM). In relaxed cluster cores, the radiative cooling time of the ICM is shorter than the age of the cluster. However, the absence of line emission associated with cooling suggests heating mechanisms that offset the cooling, with feedback from active galactic nuclei (AGNs) being the most likely source1,2. Turbulence and bulk motions, such as the oscillating ('sloshing') motion of the core gas in the cluster potential well, have also been proposed as mechanisms for heat distribution from the outside of the core3,4. Here we present X-ray spectroscopic observations of the Centaurus galaxy cluster with the X-Ray Imaging and Spectroscopy Mission satellite. We find that the hot gas flows along the line of sight relative to the central galaxy, with velocities from 130 km s‑1 to 310 km s‑1 within about 30 kpc of the centre. This indicates bulk flow consistent with core gas sloshing. Although the bulk flow may prevent excessive accumulation of cooled gas at the centre, it could distribute the heat injected by the AGN and bring in thermal energy from the surrounding ICM. The velocity dispersion of the gas is found to be only ≲120 km s‑1 in the core, even within about 10 kpc of the AGN. This suggests that the influence of the AGN on the surrounding ICM motion is limited in the cluster....
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The Astrophysical Journal 2025年1月20日
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The Astrophysical Journal Letters 2024年12月20日<jats:title>Abstract</jats:title> <jats:p>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 <jats:sc>xxv</jats:sc> He<jats:italic>α</jats:italic> and Fe <jats:sc>xxvi</jats:sc> Ly<jats:italic>α</jats:italic> 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<jats:sup>−1</jats:sup>. 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.</jats:p>
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Publications of the Astronomical Society of Japan 2024年12月4日<jats:title>Abstract</jats:title> <jats:p>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.</jats:p>
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Publications of the Astronomical Society of Japan 2024年10月3日
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The Astrophysical Journal 2024年9月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<inline-formula> <mml:math overflow="scroll"><mml:mspace width="0.25em"></mml:mspace><mml:mo>=</mml:mo><mml:mspace width="0.25em"></mml:mspace><mml:msubsup><mml:mrow><mml:mn>1600</mml:mn></mml:mrow><mml:mrow><mml:mo>‑</mml:mo><mml:mn>200</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo><mml:mn>400</mml:mn></mml:mrow></mml:msubsup><mml:mspace width="0.25em"></mml:mspace><mml:mi>km</mml:mi><mml:mspace width="0.25em"></mml:mspace><mml:msup><mml:mrow><mml:mi mathvariant="normal">s</mml:mi></mml:mrow><mml:mrow><mml:mo>‑</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msup></mml:math> </inline-formula>. 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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Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 2024年7月
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Astroparticle Physics 2024年6月
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Physical Review A 105(2) 2022年
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Journal of Astronomical Telescopes, Instruments, and Systems 7(3) 2021年
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IEEE Transactions on Nuclear Science 68(8) 2021年
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Review of Scientific Instruments 92(6) 2021年
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Astroparticle Physics 126 2021年
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Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 924 2019年
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Publications of the Astronomical Society of Japan 70(6) 2018年
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Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 806 2016年
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Journal of Geophysical Research: Space Physics 121(7) 2016年
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Publications of the Astronomical Society of Japan 68 2016年
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Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 840 2016年
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Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 831 2016年
MISC
2講演・口頭発表等
104共同研究・競争的資金等の研究課題
1-
日本学術振興会 科学研究費助成事業 2021年4月 - 2024年3月
