XRISM/Xtend Transient Search (XTS) detected an X-ray flare possibly from a K- or M-type star
ATel #17399; T. Hakamata (UOsaka), M. Mizumoto (UTEF), K. Fukushima, Y. Kanemaru, S. Ogawa, Y. Uchida, T. Yoneyama (JAXA), M. Audard (U. de Geneve), E. Behar (Technion), S. Inoue (Kyoto U.), Y. Ishihara (Chuo U.), C. Kang (Ehime U.), T. Kohmura (TUS), T. Kiyomoto (Saitama U.), H. Kuramoto (UOsaka), J. Kurashima (U. of Miyazaki), Y. Maeda (JAXA), H. Matsumoto (UOsaka), T. Matsushima (U. of Miyazaki), A. Miyamoto (UOsaka), K. Mori (U. of Miyazaki), Y. Motogami (Saitama U.), N. Nagashima (Chuo U.), T. Narita (Kyoto U.), M. Nobukawa (NUE), H. Noda (Tohoku U.), Y. Sakamoto (Tohoku U.), M. Shidatsu (Ehime U.), H. Sugai (Chuo U.), H. Takahashi (Hiroshima U.), T. Takagi (Ehime U.), S. Takatuska (UOsaka), R. Takemoto (U. of Miyazaki), Y. Terada (Saitama U.), Y. Terashima (Ehime U.), Y. Tsuboi (Chuo U.), H. Uchida (Kyoto U.), M. Yoshimoto (Ehime U.)
on 19 Sep 2025; 04:06 UT
Credential Certification: Tomokage Yoneyama (tyoneyama263@g.chuo-u.ac.jp)
Subjects: X-ray, Star, Transient, Variables
XRISM/Xtend Transient Search (XTS) detected an X-ray flare from an X-ray source XRISM J0450-5858 on 2025-09-14 TT. The source position is determined to be (R.A., Dec.) = (72.541, -58.960), with a systematic error of ∼ 40 arcsec. XRISM J0450-5858 is located approximately 4 and 32 arcsec from a Gaia source Gaia DR3 4774004897107993344 (K-type single star candidate) and Gaia DR3 4774005339488928384 (M-type single star candidate), respectively.
The flare started at 2025-09-14 at ∼02:33 TT. The flare reached its peak on 2025-09-14 at ∼05:53. The flare exponentially decayed in ∼8 × 103 sec. The flux is estimated using a power-law model. The peak flux is calculated as 1.1 × 10-13 erg s-1 cm-2 (0.4 â 10.0 keV). A systematic error is roughly estimated to be 20%.
The corresponding luminosity is 4 × 1029 erg s-1, assuming the distance to XRISM J0450-5858 of 297 pc. This distance corresponds to Gaia DR3 4774004897107993344, which is the closest source to XRISM J0450-5858.
We estimated the systematic error for the source position from the separations between the detected sources with the corresponding counterparts in the same field of view.
