TITLE: GCN CIRCULAR NUMBER: 42137 SUBJECT: GRB 251006B/EP251006a: EP-WXT detection DATE: 25/10/07 03:30:56 GMT FROM: EP Team at NAOC/CAS ep_ta@bao.ac.cn
Y.-H. I. Yin (HKU), M. H. Zhang, T. Y. Liu, H. Y. Ren and Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team:
We report on the detection of a fast X-ray transient, designated EP251006a, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient event started at T0 = 2025-10-06T20:05:04 (UTC). The position of the source is R.A. = 40.505 deg, DEC = -5.989 deg (J2000) with an uncertainty of 2.4 arcmin in radius (90% C.L. statistical and systematic). The trigger time and position of this X-ray transient are consistent with that of GRB 251006B (GCN 42131, GCN 42132).
The analysis of the WXT data shows that the event lasted for about 100 seconds with a two-pulse main emission within T0 - T0 + 10 s followed by a much weaker tail. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 2.98 x 10^20 cm^-2 and a photon index of 1.28 (-0.60/+0.64). The derived average unabsorbed 0.5-4 keV flux is 1.61 (-0.72/+0.50) x 10^-10 erg/s/cm^2. The peak flux is around 9.09 x 10^-9 erg/s/cm^2 with a fixed Galactic hydrogen column density of 2.98 x 10^20 cm^-2 and a photon index of 1.09 (-0.76/+0.84).
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).
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