TITLE: GCN CIRCULAR NUMBER: 39800 SUBJECT: EP250321a: Einstein Probe detection of an X-ray transient DATE: 25/03/21 08:04:38 GMT FROM: EP Team at NAOC/CAS ep_ta@bao.ac.cn

D. F. Hu (PMO, CAS), H. Q. Cheng (NAO, CAS), Z. H. Yang, Q. C. ZHAO (IHEP, CAS), L. Chen, W. D. Zhang (NAO, CAS) report on behalf of the Einstein Probe 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 EP250321a. The transient triggered EP-WXT (ID: 01709133009) at 2025-03-21 06:09:59 (UTC). The WXT position of the source is R.A. = 179.262 deg, DEC = 17.386 deg (J2000) with an uncertainty of 3.1 arcmin in radius (90% C.L. statistical and systematic).

A follow-up observation with the Follow-up X-ray Telescope (FXT) has been scheduled. 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).

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