TITLE:   GCN CIRCULAR
NUMBER:  41674
SUBJECT: EP250903a: Einstein Probe detection of an X-ray transient
DATE:    25/09/03 15:41:06 GMT
FROM:    EP Team at NAOC/CAS <ep_ta@bao.ac.cn>

T. Zhao, Y. J. Song(NAO, CAS), Y. J. Zhang(THU), H. Sun(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 EP250903a, which was also followed by GOTO (O'Neill et al., GCN 41672). The transient triggered EP-WXT (ID: 01709201159) at 2025-09-03T14:03:01 (UTC). The WXT position of the source is R.A. = 339.120 deg, DEC = -49.863 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. = 339.1097 deg, DEC = -49.8572 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic).

There are several stars within the FXT error circle. The stellar flare origin for this event can not be fully ruled out at this time. 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).