TITLE: GCN CIRCULAR NUMBER: 40390 SUBJECT: EP250508a: Einstein Probe detection of an X-ray transient DATE: 25/05/08 06:37:42 GMT FROM: EP Team at NAOC/CAS ep_ta@bao.ac.cn

R.D. Liang, T. Zhao, H. Q. Cheng, W. D. Zhang (NAOC, 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 EP250508a. The transient triggered EP-WXT (ID: 01709175339) at 2025-05-08T06:03:47 (UTC). The WXT position of the source is R.A. = 178.266 deg, DEC = -19.900 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. = 178.2540 deg, DEC = -19.9225 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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