XRISM/Xtend Transient Search (XTS) detected an X-ray flare from a BY Dra variable MS Ser
ATel #16683; 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 2 Jul 2024; 11:03 UT
Credential Certification: Tomokage Yoneyama (tyoneyama263@g.chuo-u.ac.jp)
Subjects: X-ray, Star, Transient, Variables
Referred to by ATel #: 16685
XRISM/Xtend Transient Search (XTS) detected an X-ray flare from an X-ray source XRISM J1558+2534 on 2024-07-01 TT. The source position is determined to be (R.A., Dec.) = (239.679 deg, +25.573 deg), with systematic error of ∼ 40 arcsec. The plausible counterpart is MS Ser, a BY Dra variable with a distance of ∼ 70 pc. MS Ser is a K- or G-type star located ∼ 9 arcsec apart from the position of XRISM J1558+2534.
Due to a bad time interval of XRISM, the flare peak was not detected, but only the decay phase was detected. Only a rough constraint, 2024-07-01 16:06 – 17:02 TT is given for the flare peak time. The flare exponentially decayed with an e-folding time of 5.5 (+1.5/-1.3) × 103 sec (90% confidence level), 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, we fit the spectrum in the flare phase with unabsorbed two APEC models with temperatures of kT1 = 0.95 (+0.09/-0.10) keV (90% confidence level) and kT2 = 2.8 (+0.8/-0.5) keV, respectively. Then, the model flux is calculated as 9.8 (+0.6/-0.7) × 10-12 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 5.9 (+/-0.4) × 10 30 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. 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.
