TITLE: GCN CIRCULAR NUMBER: 44718 SUBJECT: EP260527a: Einstein Probe detection of a fast X-ray transient DATE: 26/05/28 03:21:10 GMT FROM: EP Team at NAOC/CAS <ep_ta@bao.ac.cn> J. Yang (ZZU), B. T. Wang (YNAO, CAS), D. F. Hu (PMO, CAS), J. P. Feng, B. Zhang (USTC), D. Zhu, K. J. Zhang (YNU) and W. D. Zhang (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 EP260527a. The transient triggered EP-WXT (ID: 01709266119) at 2026-05-27T06:19:54 (UTC). The WXT position of the source is R.A. = 193.057 deg, DEC = 1.473 deg (J2000) with an uncertainty of 2.3 arcmin in radius (90% C.L. statistical and systematic). The preliminary analysis of the WXT data shows that the event started at 2026-05-27T06:16:18 (UTC) and lasted for about 200 seconds. The average WXT 0.5-4.0 keV spectrum can be fitted with an absorbed powerlaw model, with a fixed Galactic hydrogen column density of 1.57 x 10^20 cm^-2 and a photon index of 0.73(+0.44/-0.42). The unabsorbed 0.5-4.0 keV flux is 1.12(+0.33/-0.28) x 10^(-9) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. This event did not trigger the Follow-up X-ray Telescope (FXT) autonomous follow-up. A follow-up observation with the FXT was performed about 20.5 hours after the WXT detection. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 193.0519 deg, DEC = 1.4832 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 are 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/44718. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...