XRISM/Xtend Transient Search (XTS) detected an X-ray flare from a spectroscopic binary
ATel #17121; K. Fukushima, K. Hayashi, Y. Kanemaru, S. Ogawa, T. Yoshida (JAXA), M. Audard (U. de Geneve), E. Behar (Technion), S. Inoue (Kyoto U.), Y. Ishihara (Chuo U.), T. Kohmura (TUS), Y. Maeda (JAXA), M. Mizumoto (UTEF), N. Nagashima (Chuo U.), M. Nobukawa (NUE), K. Pottschmidt (UMBC, NASA GSFC, CRESST), M. Shidatsu (Ehime U.), H. Sugai (Chuo U.), Y. Terada (Saitama U.), Y. Terashima (Ehime U.), Y. Tsuboi (Chuo U.), H. Uchida (Kyoto U.), T. Yanagi (Chuo U.), T. Yoneyama (Chuo U.), M. Yoshimoto (Osaka U.)
on 31 Mar 2025; 11:27 UT
Credential Certification: Kotaro Fukushima (kxfukushima@gmail.com)
Subjects: X-ray, Transient, Variables
XRISM/Xtend Transient Search (XTS) detected an X-ray flare from an X-ray source, XRISM J1911+0509, on 2025-03-27 TT. The source position is determined to be (R.A., Dec.) = (287.733, 5.150), with a systematic error of ∼ 40 arcsec. A plausible counterpart is an X-ray source 2E 1908.4+0503, which may correspond to a spectroscopic binary UCAC4 476-091023 at 259 pc. UCAC4 476-091023 is located ∼ 5 arcsec apart from the position of XRISM J1911+0509. All statistical uncertainties in this report will be provided at a 90% confidence level unless stated otherwise.
The flare started around 2025-03-27 at 20:00 TT, peaked on 2025-03-27 at 20:54 TT, and then, exponentially decayed in 2 × 103 sec, which is derived by fitting the 0.4 – 2.0 keV light curve with a constant + burst model in the QDP software package.
In order to estimate the source flux, we fit the spectrum in the flare phase with an absorbed APEC model with a temperature of kT = 1.3 (+0.4/-0.2) keV and a hydrogen column density NH < 4 × 1021 cm-2. Then, the model flux is calculated as (6.5 +1.5/- 1.3) × 10-13 erg s-1 cm-2 (0.4 – 10.0 keV). A systematic error of roughly 20% should be added to the statistical error. Corresponding luminosity is (5.2 +1.2/-1.1) D2259 pc × 10 30 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 and their corresponding counterparts in the same field of view.
