TITLE: GCN CIRCULAR NUMBER: 45248 SUBJECT: EP260728a: Einstein Probe detection of a fast X-ray transient DATE: 26/07/29 02:47:29 GMT FROM: EP Team at NAOC/CAS <ep_ta@bao.ac.cn> G. J. Yang, J. W. Hu (NAO, CAS), H. Zhou (PMO), C. C. Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260728a. The transient triggered EP-WXT (ID: 01709276975) at 2026-07-28T16:46:27 (UTC). The on-ground analysis shows the WXT position of the source is R.A. = 302.859 deg, DEC = -31.693 deg (J2000) with an uncertainty of 2.4 arcmin in radius (90% C.L. statistical and systematic). The refined analysis of the WXT data shows that the event started at T0=2026-07-28T16:45:19 (UTC) and lasted for about 70 s before the observation was interrupted by the autonomous follow-up observation. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a hydrogen column density of 3.1 (+2.0/-1.8)×10^21 cm^-2 and a photon index of 1.63 (+0.77/-0.72). The derived average unabsorbed 0.5-4 keV flux is 4.2 (+1.6/-0.8) x 10^-9 erg/s/cm^2. The uncertainties are at the 1 sigma confidence level for the above parameters. A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 302.8558 deg, DEC = -31.7161 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). Further information will be updated when the telemetry data is received. 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/45248. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...