TITLE: GCN CIRCULAR NUMBER: 43693 SUBJECT: EP260209a: Einstein Probe detection of a fast X-ray transient DATE: 26/02/11 11:43:58 GMT FROM: EP Team at NAOC/CAS <ep_ta@bao.ac.cn> Y.J. Zhang (THU), R. Shi (PMO), Z. H. Yang, Q. C. Zhao (IHEP), G. Y. Zhao (SYSU) and Z. X. Ling (NAOC) 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 EP260209a. The EP-WXT observation started at 2026-02-09T13:44:06 (UTC). The WXT position of the source is R.A. = 159.683 deg, DEC = 28.312 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). The light curve exhibits a flare in the first 50 seconds of the WXT observation, with a 0.5--4 keV flux of approximately 7.4 × 10^-10 erg s^-1 cm^-2. The delayed report of the transient is due to its relatively low detection significance. We performed a follow-up observation with the Follow-up X-ray Telescope (FXT), starting at 2026-02-10T07:02:41 (UTC), about 17 hours after the detection. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 159.6834 deg, DEC = 28.3078 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic). The uncatalogued X-ray source has a 0.5--10 keV flux of 1.1 x 10^-13 erg s^-1 cm^-2, with a powerlaw index of 1.3 and a fixed galactic NH value (1.6 x 10^20 cm^-2). 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/43693. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...