XRISM/Xtend Transient Search (XTS) detected a flare or outburst from a new X-ray transient source candidate XRISM J2326+5843
ATel #17811; Y. Motogami (Saitama U.), H. Noda (Tohoku U.), Y. Kanemaru, A. Miyamoto, Y. Omiya, Y. Uchida, T. Yoneyama (JAXA), M. Audard (U. de Geneve), E. Behar (Technion), K. Fukushima (TUS), T. Hakamata (UOsaka), S. Inoue (Kyoto U.), Y. Ishihara (Chuo U.), C. Kang (Ehime U.), T. Kiyomoto (Saitama U.), T. Kohmura (TUS), H. Kuramoto (UOsaka), Y. Maeda (JAXA), H. Matsumoto (UOsaka), A. Miyamoto (UOsaka), M. Mizumoto (UTEF), T. Narita (RIKEN), M. Nobukawa (NUE), 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.), A. Yoshimoto (NWU), M. Yoshimoto (Ehime U.), P. P. Plucinsky (CfA)
on 25 May 2026; 07:24 UT
Credential Certification: Tomokage Yoneyama (tyoneyama263@g.chuo-u.ac.jp)
Subjects: X-ray, Transient, Variables
XRISM/Xtend Transient Search (XTS) detected a new X-ray transient source candidate XRISM J2326+5843 on an observation during 2026-05-23 to 2026-05-24 TT, whose exposure is 47 ks. The source position is determined to be (R.A., Dec.) = (351.497, 58.712), corresponding to (l, b) = (112.018, -2.337), with a systematic error of ∼ 40 arcsec. No X-ray counterpart candidate is identified within the region. One of the possible counterparts at other wavelengths is ASASSN-V J232558.05+584243.0 for optical, which is located 10 arcsec apart from the position of XRISM J2326+5843.
All statistical uncertainties in this report are provided at a 90% confidence level unless stated otherwise.
The flare started at 2026-05-24 at ∼ 12:50 TT. The flare reached its peak on 2026-05-24 at ∼ 12:50. The flare exponentially decayed in ∼ 1.8 × 104 sec.
The peak spectrum is reproduced by an absorbed APEC model, with a plasma temperature of kT = 1.9 (+0.6/-0.3) and a high absorption value of NH = 8.2 (+5.1/-4.6) × 1020 cm-2.
The absorbed flux is derived as 6.6 (+1.0/-1.0) × 10-13 erg s-1cm-2 in the energy ranges of 0.4 – 10 keV. The corresponding luminosity is 3.2 × 1030 erg s-1 by assuming the distance of 200 pc for ASASSN-V J232558.05+584243.0.
A systematic error of roughly 20% should be added to the statistical error.
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 and their corresponding counterparts in the same field of view.
