GCN Circular 45428
Subject
EP260822a: Einstein Probe detection of a fast X-ray transient
Event
Date
2026-08-23T08:30:22Z (8 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
J. P. Feng, B. Zhang (USTC), Y. Q. Zhao(USTC,PRIC), H. Sun (NAO,CAS) on behalf of the Einstein Probe (EP) team:
We report the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) onboard the Einstein Probe (EP), designated EP260822a. EP-WXT first detected the current outburst at 2026-08-22T15:16:02 (UTC), with a flux of about 4.81×10^-11 erg/cm^2/s, located at (R.A., DEC) = (14.334 deg, 11.275 deg) and (Galactic I, b) = (125.259 deg, -51.570 deg), with a 90% positional uncertainty radius of 2.6 arcmin. Short-timescale variation is observed during the ~700s WXT exposure. The transient lasts for around 350 seconds.
The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a hydrogen column density of 0.78 (-0.59/+1.26) x10^22 cm^-2, and a photon index of 3.07 (-1.75/+4.08) (90% C.L. statistical and systematic). The derived average unabsorbed 0.5-4 keV flux is 2.23 (-1.47/+54.17) x 10^-10 erg s^-1 cm^-2. There is no X-ray history detection within the WXT error circle. We also note that we can not rule out the possibility that EP260822a might be the stellar flare of the star G 2-7, which is within the WXT error circle.
Follow-up observations by EP-FXT have been scheduled. Multi-wavelength follow-up observations are encouraged to identify the nature of this likely new X-ray transient.
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).