研究者業績
基本情報
研究分野
1経歴
4-
2026年10月 - 現在
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2013年11月 - 2026年9月
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2011年4月 - 2013年10月
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2010年4月 - 2011年3月
論文
130-
The Astrophysical Journal 1001(1) 46-46 2026年4月3日Abstract The elemental abundances of the Fe-peak elements (such as Cr, Mn, Fe, and Ni) and Ti are important for understanding the environment of explosive nuclear burning for the core-collapse supernovae (CCSNe). In particular, the supernova remnant Cassiopeia A (Cas A), which is well known for its asymmetric structure, contains three “Fe-rich blobs,” and the composition of the Fe-peak elements within these structures could be related to the asymmetry of the supernova explosion. We report a highly asymmetric distribution of the Fe-peak elements in Cas A as revealed by XRISM observations. We found that the southeastern Fe-rich region has a significant Mn emission above the 4 σ confidence level, while the northwestern Fe-rich region has no clear signature. In addition to the significant difference in Mn abundance across these regions, our observations show that the Ti/Fe, Mn/Cr, and Ni/Fe ratios vary from region to region. The observed asymmetric distribution of Fe-peak elements could be produced by (1) the mixing of materials from different burning layers of the supernova, (2) the asymmetric distribution of the electron fraction in the progenitor star, and/or (3) the local dependence of the neutrino irradiation in the supernova innermost region. Future spatially resolved spectroscopy of Cas A using X-ray microcalorimeters will enable more detailed measurements of the distribution and composition of these elements, providing a unique tool for testing asymmetric supernova physics.
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UV, X-Ray, and Gamma-Ray Space Instrumentation for Astronomy XXIV 61-61 2025年9月29日
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Monthly Notices of the Royal Astronomical Society 541(2) 1403-1418 2025年6月28日ABSTRACT The Fe K$\alpha$ fluorescence line ($\sim 6.4$ keV) has been observed during solar and stellar flares. Two emission mechanisms of the Fe K$\alpha$ line, photoionization, and collisional ionization, have been discussed, and the aim of this work is to collect evidences for each mechanism employing a statistical correlation approach between the Fe K$\alpha$ line flux and rough flare properties. Here, we systematically searched the Neutron Star Interior Composition ExploreR (0.2–12 keV) archive data for the Fe K$\alpha$ line of RS Canum Venaticorum-type stars. Among our analysed 255 observation IDs with a total exposure of $\sim 700$ ks, we found 25 data sets (total $\sim 40$ ks) exhibiting the Fe K$\alpha$ emission line at 6.37–6.54 keV with its equivalent width of 44.3–578.4 eV: 18 observations during flares, six observations during unconfirmed possible flare candidates, and one at a quiescent phase. These observations indicate a positive correlation between the Fe K$\alpha$ line intensity ($L_{\rm{K \alpha } }$) and the 7.11–20 keV thermal plasma luminosity ($L_{\mathrm{HXR } }$) with its power-law index of $0.86 \pm 0.46$ (i.e. $L_{\mathrm{K \alpha } } \propto L_{\mathrm{HXR } }^{0.86\pm 0.46}$). This correlation in the range of the thermal plasma luminosity $10^{29-33}$ erg s$^{-1}$ is consistent with the photoionization origin of the line. On the other hand, the equivalent width of the Fe K$\alpha$ line ($\mathrm{EW}_{\mathrm{K \alpha } }$) has a negative correlation with the 7.11–20 keV thermal plasma luminosity with its power-law index of $-0.27 \pm 0.10$ (i.e. $\mathrm{EW}_{\mathrm{K \alpha } } \propto L_{\mathrm{HXR } }^{-0.27\pm 0.10}$). This anticorrelation is consistent with the decline of the fluorescence efficiency with increasing the stellar flare loop height. Furthermore, we found a signature of an absorption line at $6.38^{+0.03}_{-0.04}$ keV during a superflare of $\sigma$ Gem. The equivalent width of the line was $-34.7^{+2.03}_{-1.58}$ eV. We discuss the density of the Fe ions from the equivalent width using the curve of growth analysis.
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Publications of the Astronomical Society of Japan 77(Supplement_1) S154-S170 2025年6月6日Abstract Young supernova remnants (SNRs) provide crucial insights into explosive nucleosynthesis products and their velocity distribution soon after the explosion. However, these velocities are influenced by the dynamics of the circumstellar medium (CSM), which in young core-collapse SNRs originates from the progenitor’s late-phase mass loss. Cassiopeia A (Cas A), the youngest known Galactic core-collapse SNR, was studied to analyze the spatial distribution of silicon and sulfur radial velocities using two high-spectral-resolution observations from the XRISM/Resolve imaging spectrometer. Resolve’s capabilities enabled the detailed characterization of Si xiii, Si xiv, S xv, and S xvi lines, whose line shapes can be resolved and modeled using Gaussian radial velocity components. The radial velocities measured generally align with previous CCD-based results, confirming that they were not artifacts caused by blended lines or ionization variations. Modeling line profiles with two-component Gaussians improved fits in some regions, revealing distinct redshifted (back side) and blueshifted (front side) components only in a few specific areas. In most regions, however, both components were either both redshifted (north-west) or both blueshifted (south-east), consistent with the patchy ejecta shell morphology seen in optically emitting fast-moving knots. The individual line components revealed line broadening ranging from $\sigma _v \approx 200$ to $\sigma _v \approx 2000$ ${\rm km\, s^{-1 } }$. Components with $1000 \lesssim \sigma _v \lesssim 2000$ ${\rm km\, s^{-1 } }$ are consistent with previously determined reverse-shock velocities, suggesting non-equilibrated or partially equilibrated ion temperatures. Narrow components with small radial velocities found near Cas A’s projected center likely originate from shocked CSM plasma. But the low radial velocity and small $\sigma _v$ poses a challenge to identify these components with either the front side or back side of the SNR, or a blend of both sides.
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Publications of the Astronomical Society of Japan 77(Supplement_1) S144-S153 2025年5月28日Abstract The expansion structure of supernova remnants is important for understanding not only how heavy elements are distributed into space, but also how supernovae explode. The ejecta expansion structure of the young core-collapse supernova remnant Cas A is investigated, with Doppler parameter mapping of the Fe–K complex by the Resolve microcalorimeter onboard the X-ray Imaging and Spectroscopy Mission (XRISM). It is found that the Fe ejecta are blueshifted in the south-east and redshifted in the north-west, indicating an incomplete shell structure, similar to intermediate-mass elements (IMEs) such as Si and S. The Fe has a velocity shift of $\sim$1400 and $\sim$2160 km s$^{-1}$ in the north-west and south-east regions, respectively, with the error range of a few hundred km s$^{-1}$. These values are consistent with those for the IMEs in the north-west region, but larger than those for the IMEs in the south-east region, although the large error region prevented us from concluding which component has significantly higher velocity. The line broadening is larger in the center with values of $\sim$2000–3000 km s$^{-1}$, and smaller near the edges of the remnant. The radial profiles of the Doppler shift and broadening of the IMEs and Fe indicate that the Fe ejecta may expand asymmetrically as IME ejecta, although the large error regions do not allow us to confirm this. Moreover, we see little bulk Doppler broadening of the Fe lines in the north-eastern jet region whereas the IME lines exhibit significant broadening. No such narrow lines are detected in the north-west region. These findings suggest an asymmetric expansion of the ejecta potentially driven by large-scale asymmetries originating from the supernova explosion. This interpretation aligns with the large-scale asymmetries predicted by models of neutrino-driven supernova explosions.
MISC
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70(2) 2017年7月1日The Crab nebula originated from a core-collapse supernova (SN) explosion<br /> observed in 1054 A.D. When viewed as a supernova remnant (SNR), it has an<br /> anomalously low observed ejecta mass and kinetic energy for an Fe-core collapse<br /> SN. Intensive searches were made for a massive shell that solves this<br /> discrepancy, but none has been detected. An alternative idea is that the SN1054<br /> is an electron-capture (EC) explosion with a lower explosion energy by an order<br /> of magnitude than Fe-core collapse SNe. In the X-rays, imaging searches were<br /> performed for the plasma emission from the shell in the Crab outskirts to set a<br /> stringent upper limit to the X-ray emitting mass. However, the extreme<br /> brightness of the source hampers access to its vicinity. We thus employed<br /> spectroscopic technique using the X-ray micro-calorimeter onboard the Hitomi<br /> satellite. By exploiting its superb energy resolution, we set an upper limit<br /> for emission or absorption features from yet undetected thermal plasma in the<br /> 2-12 keV range. We also re-evaluated the existing Chandra and XMM-Newton data.<br /> By assembling these results, a new upper limit was obtained for the X-ray<br /> plasma mass of <~ 1Mo for a wide range of assumed shell radius, size, and<br /> plasma temperature both in and out of the collisional equilibrium. To compare<br /> with the observation, we further performed hydrodynamic simulations of the Crab<br /> SNR for two SN models (Fe-core versus EC) under two SN environments (uniform<br /> ISM versus progenitor wind). We found that the observed mass limit can be<br /> compatible with both SN models if the SN environment has a low density of <~<br /> 0.03 cm-3 (Fe core) or <~ 0.1 cm-3 (EC) for the uniform density, or a<br /> progenitor wind density somewhat less than that provided by a mass loss rate of<br /> 10-5 Mo yr-1 at 20 km s-1 for the wind environment.
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ASTROPHYSICAL JOURNAL LETTERS 837(1) 2017年3月
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日本物理学会講演概要集 72 508-508 2017年<p>NGHXTあらため、FORCE衛星は1-80 keVの広帯域X線を高感度で撮像分光し、まだ見ぬ隠されたブラックホールや超新星残骸のフィラメントでの粒子加速の探査を目指している。2016年に変更した計画の内容、検出器および望遠鏡の開発状況、およびサイエンス検討の進捗を報告する。</p>
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7 years of MAXI: monitoring X-ray Transients 2017年
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NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 831 61-64 2016年9月
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NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 831 55-60 2016年9月
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NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 831 415-419 2016年9月
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Proceedings of SPIE - The International Society for Optical Engineering 9905 2016年
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SPACE TELESCOPES AND INSTRUMENTATION 2016: ULTRAVIOLET TO GAMMA RAY 9905 2016年
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日本物理学会講演概要集 71 368-368 2016年<p>X線天文衛星「ひとみ」搭載CCDカメラ(SXI)は、200μm厚の裏面照射型PチャンネルCCDを完全空乏化させ、0.4－12 keV の軟X線帯域で38分角四方の広い視野をカバーする。SXIは軌道上での立ち上げから、冷却後の天体データ取得に至るまで、期待通りの性能を示した。我々は軌道上データを用いて、線形性・電荷転送効率・応答関数・検出効率などを較正しており、本講演ではその現状について報告する。また、可視光漏れなど軌道上で発生した事象への対策についても報告する。</p>
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JOURNAL OF INSTRUMENTATION 10 2015年6月
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UV, X-RAY, AND GAMMA-RAY SPACE INSTRUMENTATION FOR ASTRONOMY XIX 9601 2015年
担当経験のある科目(授業)
5-
物理科学課題研究 (京都大学)
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情報基礎演習 (京都大学)
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X線観測衛星による高エネルギー天文学実習 (京都大学)
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現代物理学実験 (京都大学)
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宇宙放射学ゼミナールIIＢ （X線） (京都大学)
共同研究・競争的資金等の研究課題
8-
日本学術振興会 科学研究費助成事業 2026年4月 - 2028年3月
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日本学術振興会 科学研究費助成事業 2025年4月 - 2027年3月
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日本学術振興会 科学研究費助成事業 2024年6月 - 2027年3月
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日本学術振興会 科学研究費助成事業 2022年4月 - 2026年3月
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日本学術振興会 科学研究費助成事業 2022年4月 - 2026年3月
社会貢献活動
3メディア報道
1その他
1-
2013年7月 - 2013年7月プレスリリース（朝日新聞、京都新聞、産経新聞、日本経済新聞、KBS京都）
