GCN Circular 41221

Y.-H. I. Yin (NJU), X. Mao, T. Zhao, C. C. Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team:

We report on the detection of an X-ray transient by EP-WXT through ground data analysis, designated EP250802a (ObsID:06800000790). The transient was detected at 2025-08-02 10:37:08 (UTC).

The WXT position of the source is R.A. = 303.321 deg, DEC = 24.814 deg (J2000) with an uncertainty of 3.1 arcmin (radius, 90% C.L. statistical and systematic). The transient event lasted for about 650 seconds. 

The average 0.5-4 keV spectrum can be fitted with an absorbed powerlaw model, with absorption fixed at the Galactic value of 3.5 x 10^21 cm^-2 and a photon index of 2.81 (+/-0.47). The unabsorbed average 0.5-4 keV flux is estimated to be 3.81 (-0.57, +0.67) x 10^-11 erg/s/cm2. The peak flux is about 1.16 (-0.20, +0.25) x 10^-10 erg/s/cm2. The uncertainties are at the 90% confidence level for the above parameters. 

Further FXT observations are scheduled. 

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).