TITLE: GCN CIRCULAR NUMBER: 39475 SUBJECT: EP250225a: Einstein Probe detected of a fast X-ray transient DATE: 25/02/26 04:23:32 GMT FROM: EP Team at NAOC/CAS <ep_ta@bao.ac.cn> S.Q. Jiang (NAO, CAS), B.-T. Wang (YNAO, CAS), H.Z. Wu (HUST), T. Zhao, Y.J. Song, Y. Liu (NAO, CAS) report on behalf of the Einstein Probe team: We report on the detection of a fast X-ray transient EP250225a at 2025-02-25T12:13:50 (UTC) by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The position of the source is R.A. = 141.272 deg, DEC = -4.932 deg (J2000) with an uncertainty of 2.8 arcmin (radius, 90% C.L. statistical and systematic). The transient event lasted for about 600 seconds. The average 0.5-4 keV spectrum can be fitted with an absorbed powerlaw model, with nH fixed at the Galactic value of 3.0 x 10^20 cm^-2 and a photon index of 2.5 (-0.9/+1.1). The unabsorbed average 0.5-4 keV flux is estimated to be 4.3 (-1.3/+2.1) x 10^-11 erg/s/cm2. The uncertainties are at the 90% confidence level for the above parameters. Further FXT observations are scheduled. 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). View this GCN Circular online at https://gcn.nasa.gov/circulars/39475. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...