TITLE: GCN CIRCULAR NUMBER: 41776 SUBJECT: EP250910a/GRB 250910A: EP-WXT detection of a fast X-ray transient DATE: 25/09/10 09:08:42 GMT FROM: EP Team at NAOC/CAS <ep_ta@bao.ac.cn> Q. C. Liu (THU), H. N. Yang, H. W. Pan (NAO,CAS) on behalf of the Einstein Probe team: We report on the detection of a fast X-ray transient, designated EP250910a, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient event started at 2025-09-10T03:16:04 (UTC). The position of the source is R.A. = 39.797 deg, DEC = -39.686 deg (J2000) with an uncertainty of 2.1 arcmin in radius (90% C.L. statistical and systematic). The trigger time and position of this X-ray transient are consistent with that of GRB 250910A (GCN 41769, GCN 41770). The 0.5-4 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 1.74 x 10^20 cm^-2 and a photon index of 0.8 (+0.3/-0.3) during the flare. The estimated unabsorbed 0.5-4 keV flux of the flare is 1.2 (+0.3/-0.2) x 10^(-9) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. The transient event lasts for 160 seconds. A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 39.8048 deg, DEC = -39.6966 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). 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/41776. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...