TITLE: GCN CIRCULAR NUMBER: 43253 SUBJECT: EP251229a: Einstein Probe detection of an X-ray transient DATE: 25/12/30 01:49:26 GMT FROM: EP Team at NAOC/CAS <ep_ta@bao.ac.cn> B. T. Wang (YNAO, CAS), J. P. Chen (SYSU), D. Zhu, K. J. Zhang (YNU), Y. L. Wang (NAO, CAS; ICE, CSIC-IEEC) and Z. X. Ling (NAO, 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 EP251229a. The transient triggered EP-WXT (ID: 01709250690) at 2025-12-29T19:58:49 (UTC). The WXT position of the source is R.A. =124.103 deg, DEC = 37.224 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). 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. = 124.1057 deg, DEC = 37.2073 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/43253. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...