TITLE:   GCN CIRCULAR
NUMBER:  44847
SUBJECT: EP260605a: Einstein Probe detection of a fast X-ray transient
DATE:    26/06/06 06:30:27 GMT
FROM:    EP Team at NAOC/CAS <ep_ta@bao.ac.cn>

A.Li (BNU), C. Y. Wang (THU), Z.-C. Zou (NJU), X. H. Tang (THU), H. Sun (NAO, CAS) 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 EP260605a. The transient was identified during ground-based telemetry analysis. The WXT light curve started at 2026-06-05T09:31:00 (UTC). The WXT position of the source is R.A. = 273.360 deg, DEC = -40.392 deg (J2000) with an uncertainty of 3.2 arcmin in radius (90% C.L. statistical and systematic).

The duration of the event is around 500 s. The WXT spectrum can be fitted with an absorbed power-law, with the absorption fixed at the Galactic value of 1.03 x 10^21 cm^-2, and a photon index of 1.76 (-0.58, +0.61). The unabsorbed 0.5-4 keV flux is 4.3 (-1.3, +1.6) x 10^-11 erg/s/cm2. All uncertainties are reported in 90% C.L.

We have arranged follow-up observation with the Follow-up X-ray Telescope onboard EP and will update the information upon receiving the data.

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).