TITLE:   GCN CIRCULAR
NUMBER:  37864
SUBJECT: EP241025a (GRB 241025A): EP on-board trigger and autonomous follow-up observation
DATE:    24/10/25 04:34:13 GMT
FROM:    EP Team at NAOC/CAS <ep_ta@bao.ac.cn>

D. Y. Li (NAO, CAS), Z. Y. Liu, M. Q. Huang (USTC), J. Q. Peng (IHEP, CAS), C. C. Jin (NAO, CAS) report on behalf of the Eintein Probe team:

We report on the detection of an X-ray transient detected by EP-WXT, EP241025a, which triggered the on-board processing unit at 2024-10-25T01:36:45 (UTC) (trigger ID: 01709111485). The trigger flux is estimated to be around 2e-10 erg/s/cm2 in 0.5-4 keV, assuming a spectral shape of absorbed power-law with a photon index of 2. An autonomous observation on the X-ray transient was performed by the EP-FXT about 3 minutes later, which also detected an X-ray source at R.A. = 333.6408 deg, DEC = 83.5772 deg (J2000) with an uncertainty of about 10 arcsecs (radius, 90% C.L. statistical and systematic), consistent with the position of the WXT transient within the uncertainties. The source flux is estimated to be around 5e-11 erg/s/cm2. We note that the trigger time and position of this X-ray transient are consistent with that of GRB 241025A (Swift GCN 37859, Fermi GBM GCN 37860, SVOM/GRM GCN 37863).

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).