TITLE: GCN CIRCULAR NUMBER: 42884 SUBJECT: EP251129a/GRB 251129A : Einstein Probe detection of an X-ray transient DATE: 25/11/29 05:21:00 GMT FROM: EP Team at NAOC/CAS ep_ta@bao.ac.cn

Y. Wu, Y. H. Jiang, C. Y. Dai (NJU), Y. Wang (PMO), H. C. Ding, T. Wu (AHNU), W. J. Zhang, Y. Liu (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 EP251129a. The transient triggered EP-WXT (ID: 01709248891) at 2025-11-29T03:14:23 (UTC). The WXT position of the source is R.A. = 224.294 deg, DEC = 79.301 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. = 224.3331 deg, DEC = 79.2903 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). The position of FXT is 36 arcsec from SVOM/MXT detection of GRB 251129A (Tan et al., GCN 42877), and 10 arcsec from its optical counterpart (Angulo et al., GCN 42883). 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/42884. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...