XRISM/Xtend Transient Search (XTS) detected an X-ray flare possibly from a YSO candidate
ATel #16561; T. Yoneyama (Chuo 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.), M. Yoshimoto (Osaka U.)
on 31 Mar 2024; 13:40 UT
Credential Certification: Yohko Tsuboi (tsuboi@phys.chuo-u.ac.jp)
Subjects: X-ray, Transient, Variables, Pre-Main-Sequence Star
XRISM/Xtend Transient Search (XTS) detected an X-ray flare from an X-ray source candidate XRISM J1628-4846 on 2024-03-30 TT. The source position is determined to be (R.A., Dec.) = (247.092 deg, -48.771 deg) with systematic error of ~ 1 arcmin. The possible X-ray candidate is 4XMM J162817.8-484621, corresponding to 1eRASS J162818.0-484619 and 2SXPS J162818.0-484619 (39 – 41 arcsec apart from the XTS detected). The possible IR candidate is SSTGLMC G335.2665-00.0151, corresponding to AGAL G335.267-00.016 and SDC G335.268-0.015, which is YSO candidate (44 – 48 arcsec apart from the XTS detected). The X-ray counterpart and the IR counterpart are separated with angular distance of ~ 90 arcsec, indicating that they are different objects. We could not determine which is the intrinsic counterpart for XRISM J1628-4846.
The flare start time is estimated to be 2024-03-30T17:20 TT with 90% error of (+1/-2) × 103 s by fitting the 0.4 – 2.0 keV light curve with a constant + burst model in the QDP software package. The light curve shows that the flare continues at the end of the observation (2024-03-30T19:48 TT). Therefore, the peak time and the decay time could not be estimated yet.
The spectrum in the flare phase is reproduced with a thermal plasma (APEC) model with absorption of NH < 1 × 1021 cm-2 and temperature of kT = 1.8 (+1.1/-0.4) keV.
A power-law (PL) model also reproduces the spectrum with absorption of NH = 3.5 (+3.5/-2.8) × 1021 cm-2 and photon index of Γ = 3.6 (+1.7/-1.4), which suggest the spectrum is soft.
The model flux is 1.6 (+0.4/-0.5) × 10-12 erg/s/cm2 for APEC model and 1.5 (+0.4/-1.2) × 10-12 erg/s/cm2 for PL model, respectively (0.4 – 10 keV; 90% C.L.). A systematic error of roughly 20% should be added to the statistical error. The flux of the possible X-ray counterpart was 6 × 10-14 erg/s/cm2 (4XMM J162817.8-484621; 0.2 – 12 keV in 2021), 2 × 10-13 erg/s/cm2 (1eRASS J162818.0-484619; 0.5 – 8 keV in 2020), and 1 × 10-13 erg/s/cm2 (2SXPS J162818.0-484619; 0.3 – 10 keV). The flux that XTS observed is one or two orders of magnitude larger than that of previous observations.
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 uncertainty for the source position from the separations between the detected sources with the corresponding counterparts in the same field of view. In addition, XRISM J1628-4846 was detected on the edge of CCD chips. The systematic error for the source position is thus estimated to be 1 arcmin, larger value than those we previously reported (ATel #16532 and #16558).
