TITLE: GCN CIRCULAR NUMBER: 43125 SUBJECT: EP251214b : Einstein Probe detection of a fast X-ray transient DATE: 25/12/15 15:56:40 GMT FROM: EP Team at NAOC/CAS <ep_ta@bao.ac.cn> Y. H. Jiang (NJU), Y.-H. I. Yin (HKU), Y. Q. Zhao (PRIC,USTC), W. F. Wen (SZTU), H. Q. Cheng, and H. Sun (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 EP251214b. The transient triggered EP-WXT (ID: 01709250023) at 2025-12-14T07:20:22 (UTC), and followed by COLIBRÍ telescope and LCO (GCN 43090, GCN 43117). Ground analysis shows that the WXT position of the source is R.A. = 144.358 deg, DEC = -22.884 deg (J2000) with an uncertainty of 2.2 arcmin in radius (90% C.L. statistical and systematic). Due to the earth occultation, the WXT data only shows the decay of a flare starting from 2025-12-14T07:19:13.9 and lasts for around 120 s, with a peak flux of ~2 x 10^-9 erg/s/cm^2. The average WXT 0.5 - 4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 4.02 x 10^20 cm^-2 and a photon index of 1.5 (-/+0.3). The derived average absorbed 0.5-4 keV flux is 1.1 (-/+0.2) x 10^-9 erg/s/cm^2. We also note that EP251214b was only detected from ground analysis after restoring the data during the period of earth occultation, which leads to some delays in the analysis as well as the issuing. 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/43125. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...