GCN Circular 38039

Y. F. Liang (PMO, CAS), Q. C. Liu (THU), Q. Y. Wu, D. H. Zhao, H. N. Yang, W. M. Yuan (NAO, CAS) report on behalf of the Einstein Probe team:

We report on the detection of a fast X-ray transient designated EP241101a, which was detected by EP-WXT at 2024-11-01T23:52:49 (UTC) and triggered the on-board processing unit at 2024-11-01T23:54:17 (trigger ID: 01709114858). The WXT position of EP241101a is R.A.= 37.763 deg, DEC = 22.731 deg (J2000) with an uncertainty of 2.8 arcmin (radius, 90% C.L. statistical and systematic). The light curve of the transient observed by the WXT lasts more than 100 seconds. The average 0.5-4 keV spectrum can be fitted with an absorbed power-law with a photon index of 0.9 (+0.6/-0.6) (with the column density fixed at the Galactic value of 1.5x10^21 cm^-2). The unabsorbed average flux in 0.5-4 keV is 1.2 (+0.5/-0.4) x 10^(-9) erg/s/cm^2. 

An autonomous observation was performed by the Follow-up X-ray Telescope (FXT) about 45 minutes later, the exposure time is about 1.6 ks. The delay of the FXT observation was due to the Earth obscuration. No significant source was detected by the FXT during its autonomous observation within the WXT error circle, thus we obtained a flux upper limit of 7.1 x 10^(-14) erg/s/cm^2 in the 0.5-10 keV. The quoted uncertainties are at the 90% confidence level for the above parameters. 
 
No previously known bright X-ray sources are found within the error circle around the source position. Further follow-up observations are encouraged to identify the nature of this X-ray transient.  

Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with onboard X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).