XRISM/Xtend Transient Search (XTS) detected an X-ray flare possibly from a YSO

ATel #17375; M. Yoshimoto (Ehime U.), T. Kiyomoto (Saitama U.), 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. Kohmura (TUS), 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.), 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.)
on 7 Sep 2025; 10:05 UT
Credential Certification: Tomokage Yoneyama (tyoneyama263@g.chuo-u.ac.jp)

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XRISM/Xtend Transient Search (XTS) detected an X-ray flare from an X-ray source XRISM J1044-5941 on 2025-09-05 TT. The source position is determined to be (R.A., Dec.) = (160.944, -59.678), with a systematic error of ∼ 40 arcsec. One of the plausible counterparts is a Young Stellar Object 2MASS J10434657-5940394, which is located ∼ 1 arcsec apart from the position of XRISM J1044-5941. Plausible X-ray counterparts are 2CXO J104346.5-594038, 4XMM J104348.9-594031. All statistical uncertainties in this report are provided as a 90% confidence level unless stated otherwise.

The flare started at 2025-09-05 at ∼ 02:12 TT. The flare reached its peak on 2025-09-05 at ∼ 02:27. The flare exponentially decayed in 1.1 (+0.4/-0.2) × 10⁴ sec. The peak flux is calculated as 1.3 (+0.1/-0.6) × 10^-12 erg s^-1 cm^-2 (1.0 – 10.0 keV). A systematic error of roughly 20% should be added to the statistical error. The corresponding luminosity is 5.0 (+0.4/-2.3) × 10³² erg s^-1 by assuming the distance to XRISM J1044-5941 of 1.8 kpc.

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.