9 papers
Chandra X-Ray Imaging and Spatially Resolved Spectroscopy of SN 1987A: Energy-Dependent Morphology of the Equatorial Ring
Yusuke Sakai, Shinya Yamada, Koji Mori +8
We present a systematic imaging and spatially resolved spectral study of SN 1987A using Chandra observations obtained between 1999 and 2025. By combining multiepoch ACIS and HETG d…
Formation of first star clusters under the supersonic gas flow -- III. Environmental trends and halo-to-halo scatter in the Pop III IMF
Shingo Hirano, Yusuke Sakai, Hideyuki Umeda
The first generations of stars ionised and enriched their host galaxies and seeded the growth of massive black holes. Models often assume that Pop III stellar masses in different m…
Spectral and photometric variability of SS 433 observed with XRISM and simultaneous optical and near-infrared telescopes
Yusuke Sakai, Shinya Yamada, Yuta Okada +36
We present results from coordinated multiwavelength observations of the SS 433, obtained with XRISM, optical telescopes, and near-infrared camera during 2024 April and 2025 March.…
XRISM High-resolution Spectroscopy of SS 433: Evidence of Decreasing Line-of-Sight Velocity Dispersion along the Jet
Megumi Shidatsu, Shogo Kobayashi, Yusuke Sakai +6
We report on the jet structure in SS 433 based on X-ray high resolution spectroscopy with the XRISM/Resolve. The source was observed over 5 days covering both inside and outside an…
Decadal brightening in the northeastern non-thermal filament of Cassiopeia A
Nao Kominato, Toshiki Sato, Yusuke Sakai +2
We present the decadal brightening of non-thermal emission flux in the northeastern filament of the young supernova remnant Cassiopeia A (Cas A), which highlights dynamic processes…
Arcsecond-Scale X-ray Imaging and Spectroscopy of SS 433 with Chandra HETG
Yusuke Sakai, Shinya Yamada, Haruka Sakemi +5
We present a spatial and spectral analysis of arcsecond-scale X-ray emission in SS 433 using zeroth-order data from Chandra High-Energy Transmission Grating (HETG) observations. Th…