TITLE:   GCN CIRCULAR
NUMBER:  37834
SUBJECT: EP241021a: EP detection of a fast X-ray transient
DATE:    24/10/22 07:10:45 GMT
FROM:    EP Team at NAOC/CAS <ep_ta@bao.ac.cn>

J. W. Hu (NAOC, CAS), Y. Wang (PMO, CAS), H. He, S. K. Yang (WHU), Y. H. Cheng (SWIFAR, YNU), W. M. Yuan (NAOC, CAS) on behalf of the Einstein Probe team 

We report on the detection of a fast X-ray transient, designated EP241021a, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient started at 2024-10-21T05:07:56(UTC) and lasted for around 100 seconds. The WXT position of EP241021a is R.A. = 28.852 deg, DEC = 5.957 deg (J2000) with an uncertainty of 2.4 arcmin (radius, 90% C.L. statistical and systematic). It has a peak flux of ~1 x 10^-9 erg/s/cm^2 in the 0.5-4 keV band. The average 0.5-4 keV spectrum can be fitted with an absorbed power law with a photon index of 1.48(-1.22, +1.24) (with a column density fixed at the Galactic one of 5 x 10^20 cm^-2). The derived average unabsorbed 0.5-4 keV flux is 3.3(-1.6, +4.8) x 10^(-10) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. 

No previously known bright X-ray sources are found within the error circle around the source position. Further follow-up observations are encouraged to identify the nature of this X-ray transient. 

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).