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....
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
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日本学術振興会 科学研究費助成事業 2021年4月 - 2024年3月
