GCN Circular 44956
Subject
EP260616a: EP-WXT detection of a fast X-ray transient
Event
Date
2026-06-16T16:27:09Z (8 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
D. Y. Li (NAO, CAS), J. H. Wu (GZHU), T. Y. Liu, Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe team:
We report on the detection of a fast X-ray transient, designated EP260616a, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient event started at 2026-06-16T07:05:16 (UTC). The position of the source is R.A. = 256.059 deg, DEC = -32.305 deg (J2000) with an uncertainty of 2.2 arcmin in radius (90% C.L. statistical and systematic). No onboard alert or automated X-ray follow-up observation was triggered at this position due to the low Galactic latitude. The start time and the position of the transient is consistent with that of GRB 260616B detected by Fermi/GBM (GCN 44953).
The average 0.5-4 keV spectrum can be fitted by an absorbed power law with a photon index of 1.8 (+0.3/-0.3). The column density is fixed at the Galactic value of 3.4 x 10^21 cm^-2. The derived average unabsorbed 0.5-4 keV flux is 4.1 (+/-0.5) x 10^-10 erg/s/cm^2. The peak flux is around 3.4 x 10^-9 erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
Follow-up observations by EP-FXT will be 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).