GCN Circular 43087
Subject
EP251214a: EP-WXT detection of an X-ray transient possibly associated with GRB 251214A
Event
Date
2025-12-14T08:15:25Z (21 hours ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y.-H. I. Yin (HKU), Y. H. Jiang (NJU), Y. Q. Zhao (PRIC, USTC), W. F. Wen (SZTU), H. Q. Cheng, and H. Sun (NAOC) 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 EP251214a. The source, with a signal-to-noise ratio of 6, did not trigger the WXT on-board trigger unit. The observation started at 2025-12-14T02:27:01 (UTC) and lasted for 3043 seconds. The WXT position of the source is R.A. = 148.471 deg, DEC = 21.053 deg (J2000) with an uncertainty of 3.1 arcmin in radius (90% C.L. statistical and systematic).
The average WXT 0.5 - 4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 2.82 x 10^20 cm^-2 and a photon index of 1.84 (-/+0.94). The derived average unabsorbed 0.5-4 keV flux is 1.05 (-0.42/+0.70) x 10^-11 erg/s/cm^2.
The position of EP251214a is around 4.86 deg away from GRB 251214A reported by the Fermi GBM Team (GCN 43085), and the observation was carried out around 2 hours after the GRB trigger. Given the temporal proximity and spatial consistency, we thus consider the EP-WXT detection the possible X-ray afterglow of GRB 251214A. EP-FXT follow-up observation has been arranged.
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).