XRISM/Xtend Transient Search (XTS) detects a variable source XRISM J1122-5907

ATel #17301; Y. Motogami (Saitama U.), M. Shidatsu (Ehime U.), K. Fukushima, Y. Kanemaru, S. Ogawa (JAXA), M. Audard (U. de Geneve), E. Behar (Technion), T. Hakamata (Osaka U.), S. Inoue (Kyoto U.), Y. Ishihara (Chuo U.), C. Kang (Ehime U.), T. Kohmura (TUS), H. Kuramoto (Osaka U.), J. Kurashima (U. of Miyazaki), Y. Maeda (JAXA), H. Matsumoto (Osaka U.), T. Matsushima (U. of Miyazaki), A. Miyamoto (Osaka U.), M. Mizumoto (UTEF), K. Mori (U. of Miyazaki), T. Kiyomoto (Saitama U.), N. Nagashima (Chuo U.), T. Narita (Kyoto U.), M. Nobukawa (NUE), H. Noda (Tohoku U.), Y. Sakamoto (Tohoku U.), H. Sugai (Chuo U.), H. Takahashi (Hiroshima U.), T. Takagi (Ehime U.), S. Takatuska (Osaka U.), R. Takemoto (U. of Miyazaki), Y. Terada (Saitama U.), Y. Terashima (Ehime U.), Y. Tsuboi (Chuo U.), H. Uchida (Kyoto U.), T. Yoneyama (Chuo U.), M. Yoshimoto (Ehime U.), D. J. Patnaude (SAO)
on 23 Jul 2025; 14:14 UT
Credential Certification: Kotaro Fukushima (kxfukushima@gmail.com)

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XRISM/Xtend Transient Search (XTS) detected a variable X-ray source XRISM J1122-5907 in the observation conducted for 57 ks from 2025-7-21 to 2025-7-23 TT. The source position is determined to be (R.A., Dec.) = (170.577, -59.123), with a systematic error of ∼ 40 arcsec. A possible counterpart is 1eRASS J112217.5-590740 or 2RXP J112218.4-590746, which is located ∼ 17 arcsec or 22 arcsec apart from the position of the source, respectively. All statistical uncertainties in this report are provided as a 90% confidence level unless stated otherwise.

During the initial ∼ 57 ks, the flux was 4.4 × 10^-14 erg s^-1 cm^-2 (0.5 – 10.0 keV). It then brightened rapidly, reaching 1.8 × 10^-13 erg s^-1 cm^-2 for a duration of ∼ 20 ks, and remained nearly constant during the final 160 ks. The averaged spectrum after the flux increase can be reproduced by an absorbed power-law model with a photon index and a column density of 1.5 (+0.4/-0.3) and < 3 × 10²² cm^-2, respectively.

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.