GCN Circular 38335

D.F. Hu, T. C. Zheng (PMO, CAS), B.-T. Wang (YNAO, CAS), M. J. Liu, H. Q. Cheng, C. C.Jin (NAO, CAS) 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, EP241126a (Obs.ID: 06800000262). The transient was first detected with WXT at around 2024-11-26 19:39:41 (UTC) and lasted for over 60 seconds. The WXT position of EP241126a is R.A.= 33.744 deg, DEC = 11.705 deg (J2000) with an uncertainty of 2.429 arcmin (radius, 90% C.L. statistical and systematic). It has a peak flux of ~2 x 10^(-8) 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 0.9 (+0.4/-0.4) (with a column density fixed at the Galactic value of 7.4 x 10^20 cm^-2). The derived average unabsorbed 0.5-4 keV flux is 3.3 (+0.9/-0.7) x 10^(-9) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. 

We have performed a target of opportunity (ToO) observation with the Follow-up X-ray Telescope (FXT) on board EP. The FXT onboard trigger shows an X-ray detection within the WXT error circle, at a position of R.A. = 33.7394 deg, DEC = 11.7001 deg (J2000) with an uncertainty of 20 arcsec (radius, 90% C.L. statistical and systematic). More details will be updated once the telemetry data is received.

No previously known bright X-ray sources are found within the error circle around the source position. More follow-up observations are encouraged to identify its nature.

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).