XRISM/Xtend Transient Search (XTS) detected an X-ray flare from 1eRASS J062850.6-585624
ATel #17402; 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; 15:22 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 J0629-5857 on 2025-09-10 TT. The source position is determined to be (R.A., Dec.) = (97.207, -58.942), with a systematic error of ∼ 40 arcsec. XRISM J0629-5857 is located approximately 12 arcsec from an X-ray source 1eRASS J062850.6-585624. 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 ∼07:08 TT. The flare reached its peak on 2025-09-10 at ∼07:41. The flare exponentially decayed in ∼7×103 sec. Although the origin of this event remains elusive, the flux is estimated using a power-law model. The peak flux is calculated as 1.1 × 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 1.3 × 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.
