TITLE: GCN CIRCULAR NUMBER: 38058 SUBJECT: EP241103a: EP observation update DATE: 24/11/03 11:46:54 GMT FROM: EP Team at NAOC/CAS ep_ta@bao.ac.cn
T. Zhao (NAO, CAS), Y. F. Liang (PMO, CAS), H. Y. Liu, W. D. Zhang (NAO, CAS) report on behalf of the Einstein Probe team:
Based on the newly received telemetry data, we update the information of the fast X-ray transient EP241103a, initially detected by EP (Zhao et al., GCN 38051). The transient flare started at 2024-11-03T01:23:37 (UTC) and lasted for around 60 seconds. The average 0.5-4 keV spectrum can be fitted with an absorbed power law with a photon index of 0.8+/-0.4 (with N_H, the neutral hydrogen column density, fixed at the Galactic value of 6.3×10^20 cm^-2). The derived average unabsorbed 0.5-4 keV flux is 3.8 (+1.1/-0.9)×10^(-9) erg/s/cm^2, while the peak flux of the flare is found to be around 1.1×10^(-8) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
The EP-FXT autonomous follow-up observation started at 2024-11-03T01:28:50 (UTC). The observation clearly unveiled an uncatalogued X-ray source located at R.A. = 27.7578 deg, DEC = 18.9566 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic). During the 2,300-second exposure, no significant variation is observed in the light curve. We fit an absorbed power law model to the 0.5-10 keV energy spectrum with N_H fixed at the Galactic value. The average flux is 6.0 (+2.3/-1.4)×10^(-13) erg/s/cm^2, and the photon index is 2.0+/-0.4. 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 X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).
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