XRISM/Xtend Transient Search (XTS) detected the second X-ray flare from a BY Dra variable MS Ser
ATel #16685; 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), M. Nobukawa (NUE), K. Pottschmidt (UMBC, NASA GSFC, CRESST), M. Shidatsu (Ehime U.), Y. Terada (Saitama U.), Y. Terashima (Ehime U.), Y. Tsuboi (Chuo U.), H. Uchida (Kyoto U.), T. Yoneyama (Chuo U.), M. Yoshimoto (Osaka U.)
on 3 Jul 2024; 10:30 UT
Credential Certification: Tomokage Yoneyama (tyoneyama263@g.chuo-u.ac.jp)
Subjects: X-ray, Star, Transient, Variables
XRISM/Xtend Transient Search (XTS) detected an X-ray flare from the X-ray source XRISM J1558+2534, whose plausible counterpart is MS Ser, on 2024-07-02 TT. This is the second flare of this source during the XRISM observation of T CrB (ATel #16683). The source position is (R.A., Dec.) = (239.679 deg, +25.573 deg), with systematic error of ∼ 40 arcsec. As mentioned below, the second flare was by a factor of 9 brighter than the first one.
Due to a bad time interval of XRISM, the start and peak time of the flare were not constrained robustly, but the source was still in the decay phase at 2024-07-02 22:54 TT. Only a rough constraint, 2024-07-02 19:17 – 20:22 TT is given for the flare peak time. The flare exponentially decayed with an e-folding time of 8.9 × 103 sec, which is derived by fitting the 0.4 – 10.0 keV light curve with a constant + burst model in the QDP software package.
In order to estimate the source flux at the maximum count rate, we fit the spectrum in the flare phase with unabsorbed two APEC models with temperatures of kT1 = 1.6 (+0.7/-0.4) keV (90% confidence level) and kT2 = 8.6 (+14.0/-2.6) keV, respectively. Then, the model flux is calculated as 8.8 (+/-0.5) × 10-11 erg s-1cm-2 (0.4 – 10.0 keV). A systematic error of roughly 20% should be added to the statistical error. Corresponding luminosity is 5.3 (+/-0.3) × 10 31 erg s-1 by assuming the distance to MS Ser of 71 pc.
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.
