TITLE: GCN CIRCULAR NUMBER: 44517 SUBJECT: EP260509a: Einstein Probe detection of an X-ray transient DATE: 26/05/10 14:32:36 GMT FROM: EP Team at NAOC/CAS <ep_ta@bao.ac.cn> C.-Y. Wang (THU), S.-Y. Fu (HUST), A. Li (BNU)Y, R. Shi (PMO), Y. Liu (NAOC, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260509a. The transient was identified during ground-based telemetry analysis. It was started at 2026-05-09T13:44:02 (UTC). The WXT position of the source is R.A. = 239.4813 deg, DEC = -18.4328 deg (J2000) with an uncertainty of 2.78 arcmin in radius (90% C.L. statistical and systematic). The duration of the event is ~ 250 s. The WXT spectrum can be fitted with an absorbed power-law, with the absorption fixed at the Galactic value of 1.05 x 10^21 cm^-2, and a photon index of 2.0 (-0.8, +0.9). The unabsorbed 0.5-4 keV flux is 6.0 (-2.0, +3.1) x 10^-11 erg/s/cm2. A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed at 2026-05-10T09:52:54. 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/44517. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...