寺田 幸功

The supermassive binary system, $η$ Carinae, is experiencing enormous wind-driven mass loss at a rate unparalleled in the rest of the Galaxy. Their wind-wind collision (WWC) continuously produces shock heated, X-ray emitting plasmas. The XRISM X-ray observatory observed the system in 2023 and 2024 when the X-ray emission began to increase toward periastron passage in 2025. This manuscript reports unprecedentedly high-resolution X-ray spectra in the iron K$α$ band between 6.2 and 7.1 keV, obtained with the Resolve X-ray microcalorimeter. The hydrogen-like (Ly$α$) and helium-like (He$α$) lines reveal three velocity components. Two of them are broadened with maximum velocities of 2000-3000 km/s, likely originating from the post-shock companion wind. The other is relatively narrow, with a Gaussian broadening of only ~290 km/s in 1 sigma, which may originate from the post-shock companion wind at the WWC stagnation point or penetrating the primary wind. The iron fluorescent lines exhibit a moderate blueshift and broadening with velocities at 100-200 km/s, consistent with the primary wind's velocity field. The spectra also confirm a Compton shoulder of the He$α$ line complex for the first time. Both fluorescing and scattering spectral profiles indicate that the binary system is seen from the companion side during these observations. The flux ratio of the Compton scattering emission to the fluorescent line suggests substantial hydrogen depletion of the primary wind, expected from CNO-cycled hydrogen nuclear fusion gas....

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 (CC SNe). In particular, the supernova remnant Cassiopeia 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 Cassiopeia 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 Cassiopeia 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....

The follow-up XRISM observation has been performed for the black hole binary MAXI J1543-564. The X-ray transient event from this object was reported and identified by MAXI in December 2025 (ATels #17552, #17559, and #17560)....

Swift/BAT triggered a new outburst of the Be X-ray binary 1A 1118-61 on 2026-01-18 (ATel #17608). Since then, X-ray and optical follow-up observations have been carried out (ATel #17613, #17616, #17620, #17626, #17627)....

The XRISM/Resolve microcalorimeter directly measured the gas velocities in the core of the Virgo Cluster, the closest example of active galactic nucleus (AGN) feedback in a cluster. This proximity allows us to resolve the kinematic impact of feedback on scales down to 5 kpc. Our spectral analysis reveals a high velocity dispersion of <inline-formula> <mml:math><mml:msub><mml:mrow><mml:mi>σ</mml:mi></mml:mrow><mml:mrow><mml:mi>v</mml:mi></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mn>26</mml:mn><mml:msubsup><mml:mrow><mml:mn>2</mml:mn></mml:mrow><mml:mrow><mml:mo>−</mml:mo><mml:mn>38</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo><mml:mn>45</mml:mn></mml:mrow></mml:msubsup></mml:math> </inline-formula> km s⁻¹ near the AGN, which steeply declines to ∼60 km s⁻¹ between 5 and 25 kpc in the northwest direction. The observed line-of-sight bulk velocity in all regions is broadly consistent with the central galaxy, M87, with a mild trend toward blueshifted motions at larger radii. Systematic uncertainties have been carefully assessed and do not affect the measurements. The central velocities, if attributed entirely to isotropic turbulence, correspond to a transonic intracluster medium at sub-6 kpc scales with 3D Mach number <inline-formula> <mml:math><mml:mn>0</mml:mn><mml:mo>.</mml:mo><mml:msubsup><mml:mn>69</mml:mn><mml:mi>-0.11</mml:mi><mml:mi>+0.14</mml:mi></mml:msubsup></mml:math> </inline-formula> and a nonthermal pressure fraction of <inline-formula> <mml:math><mml:msubsup><mml:mn>21</mml:mn><mml:mi>-5</mml:mi><mml:mi>+7</mml:mi></mml:msubsup><mml:mo>%</mml:mo></mml:math> </inline-formula>. Simple models of weak shocks and sound waves and calculations assuming isotropic turbulence both support the hypothesis that the velocity field reflects a mix of shock-driven expansion and turbulence. Compared to other clusters observed by XRISM to date, M87's central region stands out as the most kinematically disturbed, exhibiting both the highest velocity dispersion and the largest 3D Mach number, concentrated at the smallest physical scales....