TITLE: GCN CIRCULAR NUMBER: 43259 SUBJECT: EP251230a / GRB 251230A: Einstein Probe detection of an X-ray transient DATE: 25/12/30 02:47:03 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),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 EP251230a. The transient triggered EP-WXT (ID: 01709250693) at 2025-12-30T01:22:21 (UTC). The WXT position of the source is R.A. = 179.881 deg, DEC = 11.427 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. = 179.8996 deg, DEC = 11.4361 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). No significant X-ray source is detected within the 20 arcsec radius of the EP-FXT position. The position of FXT is 10.1 arcsec from Swift/XRT detection of GRB 251230A (Lanava et al., GCN 43252), and 11.6 arcsec from its optical counterpart (Li et al., GCN 43255). 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/43259. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...