GCN Circular 38211

Z. Y. Liu, M. Q. Huang (USTC), C. Y. Dai (NJU), X. P. Xu, M. H. Zhang, W. Yuan (NAO, CAS) report on behalf of the Einstein Probe team:

We report on the detection of an X-ray transient detected by EP-WXT, EP241113a, which triggered the on-board processing unit (trigger ID: 01709120178) at 2024-11-13T19:12:53 (UTC). The telemetry data show that the flare started at 2024-11-13T19:09:19 (UTC) . The 0.5-4 keV spectrum can be fitted using an absorbed power law with a photon index of 1.3 +/- 0.2 (with column density fixed to the Galactic value of 2.6e20 cm^-2). The derived average flux is estimated to be around 5.57 (+1.26/-0.76 ) ×10^(-10) erg/s/cm2 in 0.5-4 keV.

An autonomous observation on the X-ray transient was performed by the EP-FXT about 2 minutes later, which detected an uncatalogued X-ray source at R.A. = 131.9964 deg, DEC = 52.3815 deg (J2000) with an uncertainty of about 10 arcsecs (radius, 90% C.L. statistical and systematic), consistent with the position of the WXT transient within the uncertainties. During the 5000-second exposure, a significant decline is observed in the light curve. We fit an absorbed power law model to the 0.5-10 keV spectra with N_H fixed at the Galactic value. The average flux is 2.5 (+0.3/-0.2)×10^(-11) erg/s/cm^2, and the photon index is 2.40+/-0.17. 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).