GCN Circular 38426

C. Zhou(HUST), G. Y. Zhao(SYSU), X. Mao, R. D. Liang, W. Yuan (NAO,CAS) report on behalf of the Einstein Probe team:

We report on the detection of a fast X-ray transient detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, EP241202b (Obs. ID: 08500000223). The transient was first detected with WXT at around 2024-12-02 15:12:55 (UTC) and lasted for over 140 seconds. The WXT position of EP241202b is R.A.= 45.302 deg, DEC = 2.441 deg (J2000) with an uncertainty of 2.6 arcmin (radius, 90% C.L. statistical and systematic). It has a peak flux of 1.4 x 10^(-9) erg/s/cm^2 in the 0.5-4 keV band. The average 0.5-4 keV spectrum can be fitted with an absorbed power law with a photon index of 1.06 (+0.43/-0.41) (with a column density fixed at the Galactic value of 9.5 x 10^20 cm^-2). The derived average unabsorbed 0.5-4 keV flux is 5.4 (+2.0/-1.6) x 10^(-10) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. No previously known X-ray sources are found within the error circle around the source position.

We plan to perform a target of opportunity observation with the Follow-up X-ray Telescope (FXT) on board EP. Further follow-up observations are encouraged to explore the origin of EP241202b.

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).