TITLE: GCN CIRCULAR NUMBER: 38211 SUBJECT: EP241113a: EP on-board trigger and autonomous follow-up observation DATE: 24/11/14 04:21:43 GMT FROM: EP Team at NAOC/CAS ep_ta@bao.ac.cn
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).
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