XRISM/Xtend Transient Search (XTS) detected an X-ray flare from 1eRASS J063125.7-584856 or 2SXPS J063124.2-584845
ATel #17403; T. Narita (Kyoto U.), T. Kohmura (TUS), K. Fukushima, Y. Kanemaru, S. Ogawa, Y. Uchida, T. Yoneyama (JAXA), M. Audard (U. de Geneve), E. Behar (Technion), T. Hakamata (UOsaka), S. Inoue (Kyoto U.), Y. Ishihara (Chuo U.), C. Kang (Ehime U.), 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), M. Mizumoto (UTEF), K. Mori (U. of Miyazaki), Y. Motogami (Saitama U.), N. Nagashima (Chuo 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; 15:26 UT
Credential Certification: Kotaro Fukushima (kxfukushima@gmail.com)
Subjects: X-ray, Transient
XRISM/Xtend Transient Search (XTS) detected an X-ray flare from an X-ray source XRISM J0631-5849 on 2025-09-10 TT. The source position is determined to be (R.A., Dec.) = (97.865, -58.818), with a systematic error of ∼ 40 arcsec. Two X-ray sources 1eRASS J063125.7-584856 and 2SXPS J063124.2-584845 are located ∼ 17 arcsec and ∼ 33 arcsec apart from the position of XRISM J0631-5849, respectively. While positions of some objects in the Gaia DR3 catalogue are consistent with this source within uncertainty, we cannot identify one optical counterpart confidently. All statistical uncertainties in this report are provided as a 90% confidence level unless stated otherwise.
The flare started at 2025-09-10 at ∼02:00 TT. The flare reached its peak on 2025-09-10 at ∼02:25. The flare exponentially decayed in ∼2.5×103 sec. The peak flux is calculated as 4.6 × 10-12 erg s-1 cm-2 (0.4 – 10.0 keV). A systematic error of roughly 20% should be added to the statistical error. The corresponding luminosity is 5.5 × D100 pc2 × 1030 erg s-1.
We derived the above systematic error for the flux by comparing our derived values for the sources detected with XTS in several observations with those for the corresponding X-ray counterparts. 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.
