TITLE:   GCN CIRCULAR
NUMBER:  37872
SUBJECT: EP241025a (GRB 241025A): EP observations update
DATE:    24/10/25 10:20:16 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 Einstein Probe team:

The preliminary analysis of the telemetry EP-WXT data shows that the bright transient EP241025a (GRB 241025A, Swift GCN 37859, Fermi GBM GCN 37860, SVOM/GRM GCN 37863, EP GCN 37864) began at (T0) 2024-10-25T01:35:29 (UTC), and lasted for around 300 seconds, with the peak flux in 0.5-4.0 keV to be around 1e-8 erg/s/cm2. The EP-FXT autonomous observation began at T0+3min and caught the latter half of the bright transient, followed by lasting fainter emission. The ground calculated EP-FXT position is RA=333.6550 deg, DEC=83.5750 deg (J2000), with an uncertainty of 10 arcsecs (radius, 90% C.L. statistical and systematic), which is consistent with the enhanced XRT position (GCN 37868). The averaged EP-FXT spectrum can be fitted with an absorbed powerlaw, with a photon index of (1.41 +/- 0.09), and an absorption of NH= (2.2 +/- 0.4) e21 cm^(-2). The derived average unabsorbed flux in 0.5-4.0 keV is (1.6 +/- 0.7) e-10 erg/s/cm2. All the errors of the parameters quoted are at 90% C.L. 

Please note that the temporal and spectral analyses presented above are preliminary. The final results will be presented in future publications. EP-FXT will also keep monitoring this transient in the following days.

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).