GCN Circular 42482
Subject
GRB 251026A/EP251026a: Einstein Probe detection of a fast X-ray transient
Event
Date
2025-10-27T15:36:49Z (4 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
A. Li (BNU), J. H. Wu (GZHU), H. Q. Cheng and H. Sun (NAOC) on behalf of the Einstein Probe (EP) team:
We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP251026a. The ground analysis of the WXT data shows that the event started at T0=2025-10-26T08:26:33 (UTC). The WXT position of the source is R.A. = 72.663 deg, DEC = 51.775 deg (J2000) with an uncertainty of 2.1 arcmin in radius (90% C.L. statistical and systematic). This transient is temporally and spatially coincident with GRB 251026A (GCN 42454).
The analysis of the WXT data shows that the event lasted for about 500 seconds. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 3.77 x 10^21 cm^-2 and a photon index of 1.00 (-0.37/+0.38). The derived average unabsorbed 0.5-4 keV flux is 1.35 (-0.6/+0.7) x 10^-9 erg/s/cm^2. The peak flux is around 2.1 x 10^-9 erg/s/cm^2 with a fixed Galactic hydrogen column density of 3.77 x 10^21 cm^-2 and a photon index of 1.07 (-0.53/+0.55).
We note that the late release of this transient is mostly due to the delay in the data transmission. Follow-up observations with EP-FXT has been scheduled and more information will be reported when the telemetry data arrives.
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).