XRISM/Xtend Transient Search (XTS) detected an X-ray flare from XRISM J1631-4843

ATel #18037; C. Kang (Ehime U.), M. Nobukawa (NUE), T. Hakamata, Y. Kanemaru, A. Miyamoto, Y. Omiya, Y. Uchida, T. Yoneyama (JAXA), M. Audard (U. de Geneve), E. Behar (Technion), K. Fukushima (TUS), H. Iinuma (Tohoku U.), S. Inoue (Kyoto U.), Y. Ishihara (Chuo U.), S. Ishiwata (Chuo U.), M. Kikuchi (Ehime U.), T. Kiyomoto (Saitama U.), T. Kohmura (TUS), H. Kuramoto (UOsaka), Y. Maeda (JAXA), H. Matsumoto (UOsaka), A. Miyamoto (UOsaka), M. Mizumoto (UTEF), Y. Motogami (Saitama U.), H. Murakami (TGU), T. Narita (RIKEN), H. Noda (Tohoku U.), S. Ogawa (TUS), Y. Sakamoto (Tohoku U.), M. Shidatsu (Ehime U.), H. Takahashi (Hiroshima U.), T. Takagi (Ehime U.), S. Takatsuka (UOsaka), F. Takisawa (Ehime U.), Y. Terada (Saitama U., JAXA), Y. Terashima (Ehime U.), Y. Tsuboi (Chuo U.), H. Uchida (Kyoto U.), T. Usuki (Ehime U.), A. Yoshimoto (NWU), M. Yoshimoto (Ehime U.), P. Pradhan (ERAU)
on 12 Sep 2026; 13:08 UT
Credential Certification: Masayoshi Nobukawa (nobukawa@cc.nara-edu.ac.jp)

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XRISM/Xtend Transient Search (XTS) detected an X-ray flare from an X-ray source XRISM J1631-4843 on 2026-09-02 TT. The source position is determined to be (R.A., Dec.) = (247.836, -48.718), with a systematic error of ∼ 40 arcsec. A plausible counterpart is an X-ray source 2SXPS J163120.2-484307 located ∼ 4 arcsec apart from the position of XRISM J1631-4843, respectively. All statistical uncertainties in this report are provided as a 90% confidence level unless stated otherwise.

The flare started at 2026-09-02 at ∼ 01:53 TT. The flare reached its peak on 2026-09-02 at ∼ 03:01. The flare exponentially decayed in ∼ 10⁴ sec. The averaged spectrum of the entire observation is reproduced with an absorbed power-law model, with an absorption of NH = 1.4 ^+0.8_-0.7 × 10²¹ cm^-2 and a photon index of Γ = 2.8 ^+0.3_-0.3. The peak flux is calculated as ∼ 4.3 ^+0.3_-0.5 × 10^-13 erg s^-1 cm^-2 (0.4 – 10.0 keV). This corresponds to a luminosity of ∼ 4.5 ^+0.3_-0.5 × 10²⁹ erg s^-1, assuming a distance of 93 pc to UCAC4 207-119661, the proposed optical counterpart. A systematic error of roughly 20% should be considered for all the fluxes calculated above.