Curriculum Vitaes
Profile Information
- Affiliation
- Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency
- Degree
- 博士（理学）
- Researcher number
- 90982108
- J-GLOBAL ID
- 202301005251755990
- researchmap Member ID
- R000051605
Research History
2-
Apr, 2023 - Present
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Apr, 2019 - Sep, 2022
Education
3-
Apr, 2019 - Mar, 2023
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Apr, 2017 - Mar, 2019
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Apr, 2013 - Mar, 2017
Committee Memberships
1-
Sep, 2019 - Jun, 2021
Awards
3Papers
39-
UV, X-Ray, and Gamma-Ray Space Instrumentation for Astronomy XXIV, 61-61, Sep 18, 2025
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UV, X-Ray, and Gamma-Ray Space Instrumentation for Astronomy XXIV, 51-51, Sep 18, 2025
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Optics for EUV, X-Ray, and Gamma-Ray Astronomy XII, 19-19, Sep 18, 2025
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Journal of Astronomical Telescopes, Instruments, and Systems, 11(04), Aug 21, 2025
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Publications of the Astronomical Society of Japan, Aug 18, 2025Abstract We report on a detailed spectroscopic study of the gas dynamics and hydrostatic mass bias of the galaxy cluster Abell 2029, utilizing high-resolution observations from XRISM Resolve. Abell 2029, known for its cool core and relaxed X-ray morphology, provides an excellent opportunity to investigate the influence of gas motions beyond the central region. Expanding upon prior studies that revealed low turbulence and bulk motions within the core, our analysis covers regions out to the scale radius $R_{2500}$ (670 kpc) based on three radial pointings extending from the cluster center toward the northern side. We obtain accurate measurements of bulk and turbulent velocities along the line of sight. The results indicate that non-thermal pressure accounts for no more than 2% of the total pressure at all radii, with a gradual decrease outward. The observed radial trend differs from many numerical simulations, which often predict an increase in non-thermal pressure fraction at larger radii. These findings suggest that deviations from hydrostatic equilibrium are small, leading to a hydrostatic mass bias of around 2% across the observed area.
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Publications of the Astronomical Society of Japan, Aug 18, 2025Abstract We present an analysis of high-resolution spectra from the shock-heated plasmas in SN 1987A, based on an observation using the Resolve instrument onboard the X-Ray Imaging and Spectroscopy Mission (XRISM). The 1.7–10 keV Resolve spectra are accurately represented by a single-component, plane-parallel shock plasma model, with a temperature of $2.84_{-0.08}^{+0.09}$ keV and an ionization parameter of $2.64_{-0.45}^{+0.58}$ × $10^{11}\,\,{\rm s\,\, cm}^{-3}$. The Resolve spectra are also well reproduced by the 3D magneto-hydrodynamic simulation presented by Orlando et al. (2020, A&A, 636, A22) suggesting substantial contribution from the ejecta. The metal abundances obtained with Resolve align with the Large Magellanic Cloud value, indicating that the X-rays in 2024 originate from “non-metal-rich” shock-heated ejecta and the reverse shock has not reached the inner metal-rich region of ejecta. Doppler widths of the atomic lines from Si, S, and Fe correspond to velocities of 1500–1700 km s$^{-1}$, where the thermal broadening effects in this non-metal-rich plasma are negligible. Therefore, the line broadening seen in Resolve spectra is determined by the large bulk motion of ejecta. For reference, we determined a $90\%$ upper limit on non-thermal emission from a pulsar wind nebula at $4.3 \times 10^{-13}$ erg cm$^{-2}$ s$^{-1}$ in the 2–10 keV range, aligning with NuSTAR findings by Greco et al. (2022, ApJ, 931, 132). Additionally, we searched for the $^{44}$Sc K line feature and found a $1\sigma$ upper limit of $1.0 \times 10^{-6}$ photons cm$^{-2}$ s$^{-1}$, which translates to an initial $^{44}$Ti mass of approximately $2 \times 10^{-4}\, M_{\odot }$, consistent with previous X-ray to soft gamma-ray observations (Boggs et al. 2015, Science, 348, 670; Grebenev et al. 2012, Nature, 490, 373; Leising 2006, ApJ, 651, 1019).
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Monthly Notices of the Royal Astronomical Society: Letters, 543(1) L6-L7, Aug 12, 2025
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The Astrophysical Journal Letters, 988(2) L58-L58, Jul 28, 2025Abstract 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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Journal of Astronomical Telescopes, Instruments, and Systems, 11(04), Jul 4, 2025
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The Astrophysical Journal Letters, 985(1) L20-L20, May 19, 2025Abstract The XRISM Resolve microcalorimeter array measured the velocities of hot intracluster gas at two positions in the Coma galaxy cluster: squares at the center and at 6 (170 kpc) to the south. We find the line-of-sight velocity dispersions in those regions to be σ z = 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, Δv z = 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, May 14, 2025Abstract We present a summary of the in-orbit performance of the soft X-ray imaging telescope Xtend onboard the X-Ray Imaging and Spectroscopy Mission (XRISM), based on in-flight observation data, including first-light celestial objects, calibration sources, and results from the cross-calibration campaign with other currently operating X-ray observatories. XRISM/Xtend has a large field of view of ${38{^{\prime }_{. } }5}$ $\times$ ${38{^{\prime }_{. } }5}$, covering an energy range of 0.4–13 keV, as demonstrated by the first-light observation of the galaxy cluster Abell 2319. It also features an energy resolution of 170–180 eV at 6 keV, which meets the mission requirement and enables us to resolve He-like and H-like Fe K$\alpha$ lines. Throughout the observation during the performance verification phase, we confirm that two issues identified in the Soft X-ray Imager (SXI) onboard the previous Hitomi mission—light leakage and crosstalk events—are addressed and suppressed in the case of Xtend. A joint cross-calibration observation of the bright quasar 3C 273 results in an effective area measured to be $\sim$420 cm$^{2}$ at1.5 keV and $\sim$310 cm$^{2}$ at 6.0 keV, which matches values obtained in ground tests. We also continuously monitor the health of Xtend by analyzing overclocking data, calibration source spectra, and day-Earth observations; the readout noise is stable and low, and contamination is negligible even one year after launch. A low background level compared with other major X-ray instruments onboard satellites, combined with the largest grasp ($\Omega _{\rm eff}\sim 60$ cm$^2$ deg$^2$) of Xtend, will not only support Resolve analysis, but also enable significant scientific results on its own. This includes near-future follow-up observations and transient searches in the context of time-domain and multi-messenger astrophysics.
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Publications of the Astronomical Society of Japan, 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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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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Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray, 53-53, Aug 22, 2024
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Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray, 55-55, Aug 22, 2024
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Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray, 232-232, Aug 21, 2024
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Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray, 52-52, Aug 21, 2024
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Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray, 197-197, Aug 21, 2024
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Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray, 218-218, Aug 21, 2024
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Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray, 284-284, Aug 21, 2024
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Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray, 282-282, Aug 21, 2024
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Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray, 89-89, Aug 21, 2024
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Journal of Astronomical Telescopes, Instruments, and Systems, 9(03), Sep 12, 2023
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EUV and X-ray Optics: Synergy between Laboratory and Space VIII, Jun 8, 2023
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Publications of the Astronomical Society of Japan, 75(1) 128-152, Dec 12, 2022Abstract A model of geocoronal solar wind charge exchange (SWCX) emission was built and compared to five Suzaku detections of bright geocoronal SWCX events. An exospheric neutral hydrogen distribution model, charge exchange cross-sections, solar wind ion data taken with the ACE and WIND satellites, and magnetic field models of the Earth’s magnetosphere are all combined in order to predict time-variable geocoronal SWCX emission depending on line-of-sight directions of the Suzaku satellite. The modeled average intensities of O vii emission lines were consistent with the observed ones within a factor of three in four out of the five cases except for an event in which a line-of-sight direction was toward the night side of the high-latitude magnetosheath and a major geomagnetic storm was observed. Those of O viii emission lines were underestimated by a factor of three or more in all five cases. On the other hand, the modeled O vii and O viii light curves reproduced the observed ones after being scaled by ratios between the observed and modeled average intensities. In particular, short-term variations due to line-of-sight directions traversing cusp regions during an orbital motion of the Suzaku satellite were reproduced. These results are discussed in the context of model uncertainties.
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Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray, Aug 31, 2022
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Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray, Aug 31, 2022
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Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray, Aug 31, 2022
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Optics Express, 30(14) 25195-25195, Jun 27, 2022We have been developing a light-weight X-ray telescope using micro electro mechanical systems technologies for future space missions. Micropores of 20 µm width are formed in a 4-inch Si wafer with deep reactive ion etching, and their sidewalls are used as X-ray reflection mirrors. The flatness of the sidewall is an important factor to determine the imaging performance, angular resolution. It is known that hydrogen annealing is effective to smooth a Si surface. We tested 150 hour annealing to achieve the ultimately smooth sidewalls. After 50 hour, 100 hour, and 150 hour annealing, the angular resolution improved 10.3, 4.0, and 2.6 arcmin in full width at half maximum (FWHM) and 17.0, 14.5, and 10.8 arcmin in half-power width (HPW). In spite of this improvement, the edge shapes of the sidewall were rounded. Therefore, both edges of the sidewall were ground and polished, and then the angular resolution was improved further to 3.2 arcmin (FWHM) and 5.4 arcmin (HPW).
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Publications of the Astronomical Society of Japan, 73(3) 504-518, Mar 16, 2021Abstract X-ray emission generated through solar-wind charge exchange (SWCX) is known to contaminate X-ray observation data, the amount of which is often significant or even dominant, particularly in the soft X-ray band, when the main target consists of comparatively weak diffuse sources, depending on the space weather during the observation. In particular, SWCX events caused by interplanetary coronal mass ejections (ICMEs) tend to be spectrally rich and to provide critical information about the metal abundance in the ICME plasma. We analyzed the SN1006 background data observed with Suzaku on 2005 September 11 shortly after an X6-class solar flare, signatures of which were separately detected together with an associated ICME. We found that the data include emission lines from a variety of highly ionized ions generated through SWCX. The relative abundances of the detected ions were found to be consistent with those in past ICME-driven SWCX events. Thus, we conclude that this event was ICME driven. In addition, we detected a sulfur xvi line for the first time as one from an SWCX emission, which suggests that it is the most spectrally rich SWCX event ever observed. We suggest that observations of ICME-driven SWCX events can provide a unique probe to study the population of highly ionized ions in the plasma, which is difficult to measure in currently available in situ observations.
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Space Telescopes and Instrumentation 2020: Ultraviolet to Gamma Ray, Dec 13, 2020
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Applied Physics Express, 13(8) 087001-087001, Aug 1, 2020
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Journal of Astronomical Telescopes, Instruments, and Systems, 6(02) 1-1, Jun 30, 2020
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Applied Optics, 58(19) 5240-5240, Jun 28, 2019
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TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, AEROSPACE TECHNOLOGY JAPAN, 17(4) 477-482, 2019
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Publications of the Astronomical Society of Japan, 71(1), Jan 1, 2019
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Japanese Journal of Applied Physics, 57(6S1) 06HJ11-06HJ11, May 18, 2018
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Applied Optics, 57(12) 3237-3237, Apr 19, 2018
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Japanese Journal of Applied Physics, 56(6S1) 06GN04-06GN04, May 10, 2017
Misc.
64Presentations
35-
10th International Conference on X-ray Optics and Applications
Professional Memberships
6-
Jul, 2023 - Present
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Dec, 2020 - Present
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May, 2019 - Present
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Jul, 2017 - Present
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Jun, 2017 - Present
Research Projects
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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, Apr, 2019 - Mar, 2022
Industrial Property Rights
1Academic Activities
1-
Peer reviewPublications of the Astronomical Society of Japan
Media Coverage
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ISAS GATE, ISAS Research Information Portal, ISAS people, Jan 22, 2024 Internet
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American Association for the Advancement of Science, EurekAlert!, Jan 28, 2023 Internet
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American Association for the Advancement of Science, EurekAlert!, Jul 16, 2022 Internet
