TITLE:   GCN CIRCULAR
NUMBER:  42816
SUBJECT: EP251124a: Einstein Probe detection of an X-ray transient
DATE:    25/11/24 13:17:56 GMT
FROM:    EP Team at NAOC/CAS <ep_ta@bao.ac.cn>

H.Zhou (PMO, CAS), J. -Y. Cao (IHEP), H.-N. Yang, and Z.-X. Ling (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 EP251124a. The transient triggered EP-WXT (ID: 01709248862) at 2025-11-24T11:10:05 (UTC). The WXT position of the source is R.A. = 43.732 deg, DEC = 41.577 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. According to the FXT onboard alert, which provided coordinates calculated autonomously on board the satellite, FXTA detected an X-ray source and FXTB detected two X-ray sources (denoted as FXTB-1 and FXTB-2) within the WXT error circle. Their coordinates (J2000) are:

FXTA: R.A. = 43.7117 deg, DEC = 41.5715 deg

FXTB-1: R.A. = 43.7188 deg, DEC = 41.5692 deg
FXTB-2: R.A. = 43.7061 deg, DEC = 41.6121 deg

All FXT localizations are reported with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). FXTB-1 is consistent with the source detected by FXTA. 

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).