XRISM/Xtend Transient Search (XTS) detected an X-ray flare from a plausible optical counterpart LP 593-21
ATel #16532; M. Yoshimoto (Osaka U.), K. Hayashi, Y. Kanemaru, S. Ogawa, T. Yoshida (JAXA), K. Akasu (Chuo U.), M. Audard (U. de Geneve), E. Behar (Technion), S. Inoue (Kyoto U.), T. Kohmura (TUS), Y. Maeda (JAXA), M. Mizumoto (UTEF), N. Nemoto (Chuo U.), 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.)
on 15 Mar 2024; 13:38 UT
Credential Certification: Yohko Tsuboi (tsuboi@phys.chuo-u.ac.jp)
Subjects: X-ray, Binary, Star, Transient, Variables
Referred to by ATel #: 16561
XRISM/Xtend Transient Search (XTS) detected an X-ray flare from a new X-ray source candidate XRISM J0335+0025 at 2024-03-09 TT. The source position is determined to be (R.A., Dec.) = (53.897 deg, 0.422 deg) with a systematic uncertainty of ~ 40 arcsec.
No corresponding source is found in X-ray source catalogs within 2 arcmin, while a plausible optical counterpart, LP 593-21, an M3.9 dwarf binary, is located ~ 15 arcsec apart from the XRISM source position. The distance from the earth to LP 593-21 is estimated to be ~ 100 pc with Gaia DR3.
The flare peaks at 2024-03-08 14:15 TT (with an uncertainty of 300 s in 90% confidence level) and exponentially decays with an e-folding time of (1.0 +/-0.5) × 103 sec (90% C.L.), which is derived by fitting the 0.4 – 2.0 keV light curve with a constant + burst model in the QDP software package. The spectrum in the flare phase is reproduced with a thermal plasma model with a temperature of kT = (2.1 +0.8/-0.6) keV (90% C.L.). The flux in the flare phase is (1.1 +/-0.3) × 10-12 erg/s/cm2 (0.4 – 10 keV; 90% C.L.). A systematic error of roughly 20% should be added to the statistic error. The corresponding luminosity is (1.3 +/-0.4) × 1030 erg/s at 100 pc, assuming the source is LP 593-21.
We derived the above systematic error for the average flux by comparing our derived values for the sources detected with XTS in several observations and those for the corresponding X-ray counterparts.
We estimated the systematic uncertainty for the source position from the separations between the detected sources and the corresponding counterparts in the same field of view.
