TITLE: GCN CIRCULAR NUMBER: 40154 SUBJECT: EP250416a: Einstein Probe detection of an X-ray transient DATE: 25/04/17 03:08:20 GMT FROM: EP Team at NAOC/CAS ep_ta@bao.ac.cn

G.Y. Zhao (SYSU), C. Zhou (HUST), X.L. Chen, K. Chatterjee (YNU), H. Zhou (PMO, CAS) and C.C. Jin (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 EP250416a. The transient triggered EP-WXT (ID: 01709135021) at 2025-04-16T17:53:59 (UTC). The WXT position of the source is R.A. = 256.402 deg, DEC = 25.768 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. = 256.4228 deg, DEC = 25.7755 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 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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