Profile Information
- Affiliation
- Assistant professor, Institute of Space and Astronautical Science, Japan Aerospace Exploration AgencyAssistant professor, Space and Astronautical Science program, The Graduate University for Advanced Studies
- Degree
- Ph. D.(Mar, 1998, Kyoto University)master's degree(Mar, 1995, Kyoto University)
- Researcher number
- 80342624
- ORCID ID
https://orcid.org/0000-0002-9099-5755- J-GLOBAL ID
- 202001011170717781
- researchmap Member ID
- R000011919
Papers
234-
Monthly Notices of the Royal Astronomical Society: Letters, 540(1) L34-L40, Mar 19, 2025ABSTRACT 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 ($\sim$15–80 keV) balloon-borne Compton-scattering polarimeter in July 2024. The polarization parameters are determined using a Bayesian analysis of Stokes parameters obtained from X-ray scattering angles. Well-constrained ($\sim 8.5\sigma$) results are obtained for the polarization of the $\sim$19–64 keV signal integrated over all pulsar phases: PD = (25.1$\pm$2.9) per cent and PA = (129.8$\pm 3.2)^\circ$. In the off-pulse (nebula-dominated) phase range, the PD is constrained at $\sim 4.5\sigma$ 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$^{+18.2}_{-28.5}$) per cent and PA = (156.0 $\pm$ 21.7)$^\circ$, while for the second peak (inter-pulse), PD = (0.0$^{+33.6}_{-0.0}$) per cent and PA = (154.5 $\pm$ 34.5)$^\circ$. 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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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.
Misc.
40-
日本物理学会講演概要集(CD-ROM), 78(2), 2023
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大気球シンポジウム: 2022年度 = Balloon Symposium: 2022, Nov, 2022大気球シンポジウム 2022年度（2022年11月7-8日. ハイブリッド開催（JAXA相模原キャンパス& オンライン)) Balloon Symposium 2022 (November 7-8, 2022. Hybrid(in-person & online) Conference (Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS)), Sagamihara, Kanagawa Japan 著者人数: 87名 資料番号: SA6000177030 レポート番号: isas22-sbs-030
Presentations
5-
Optics & Photonics Japan 2023, Nov 29, 2023 Invited
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44th COSPAR Scientific Assembly, 2022
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nuclear burning in massive stars – towards the formation of binary black holes –, Jul 28, 2021
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Space Telescopes and Instrumentation 2020: Ultraviolet to Gamma Ray, Dec 19, 2020
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The 15th Symposium of Japanese Research Community on X-ray Imaging Optics, Oct 26, 2019 Invited
Teaching Experience
6-
Sep, 2023 - Mar, 2024
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Apr, 2021 - Mar, 2022Space Science Review (The Graduate University for Advanced Studies)
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Oct, 2019 - Mar, 2020Space Science Review (The Graduate University for Advanced Studies)
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Oct, 2009 - Mar, 2010Applied Physics (Chuo University)
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Apr, 2009 - Sep, 2009Astrophysics (Chuo University)
Professional Memberships
4-
Jul, 1998 - Present
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Mar, 1998 - Present
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Jan, 1997 - Present
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Aug, 1993 - Present
Research Projects
11-
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, 2025
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Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A), Japan Society for the Promotion of Science, Apr, 2020 - Mar, 2023
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科学研究費助成事業 挑戦的研究(萌芽), 日本学術振興会, Jun, 2019 - Mar, 2022
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科学研究費助成事業 新学術領域研究(研究領域提案型), 日本学術振興会, Apr, 2013 - Mar, 2015
