GCN Circular 37848
Subject
EP241021a: EP-FXT follow-up observation update
Date
2024-10-23T15:51:34Z (8 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y. Wang (PMO, CAS), H. He, S. K. Yang (WHU), Y. H. Cheng (SWIFAR, YNU), J. W. Hu, X. P. Xu, W. Yuan (NAO, CAS) on behalf of the Einstein Probe team
Following the detection of the fast X-ray transient EP241021a (Hu et al., GCN 37834), we performed an observation of EP241021a with the Follow-up X-ray Telescope (FXT) on board Einstein Probe. The observation started at 2024-10-22T17:44:27 (UTC), about 36.5 hours after the EP-WXT detection, with an exposure time of 3023 seconds. An uncatalogued X-ray source is detected at R.A. = 28.8483 deg, DEC = 5.9395 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic). The average FXT spectrum in 0.5-10 keV band can be fitted by an absorbed power law with a photon index of 1.57(+0.53/-0.49) (with a column density fixed at the Galactic one of 5 x 10^20 cm^-2), giving an average unabsorbed flux of 2.3(+1.4/-0.8) x 10^-13 erg/s/cm^2. We consider this FXT source to be the afterglow of the X-ray transient EP241021a, which is 5 arcsec away from the likely optical counterpart (Fu et al., GCN 37840, 37842, Li et al., GCN 37844, Ror et al., GCN 37845, Li et al., GCN 37846).
Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).