TITLE: GCN CIRCULAR NUMBER: 38477 SUBJECT: EP241208a: EP detection of a fast X-ray transient DATE: 24/12/09 06:10:36 GMT FROM: EP Team at NAOC/CAS ep_ta@bao.ac.cn

Y. L. Wang (NAO, CAS), Y. Wang (PMO, CAS), H. L. Peng (NNU), W. D. Zhang (NAO,CAS) report 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, designated EP241208a. The transient triggered the on-board processing unit at 2024-12-08 16:36:13 (UTC) and lasted for ~ 50 seconds (trigger ID: 01709128715). The WXT position of EP241208a is R. A.= 127.812 deg, DEC = 49.082 deg (J2000) with an uncertainty of 4 arcmin (radius, 90% C.L. statistical and systematic). We analysed the late arrived telemetry data and the average 0.5-4 keV spectrum can be fitted with an absorbed powerlaw with a photon index of 1.29 (+0.93/-0.88) (with the column density fixed at the Galactic value of 4.20 x 10^20 cm^-2). The derived average unabsorbed 0.5-4 keV flux is 6.57 (+4.73/-2.49) x 10^(-10) erg/s/cm^2.

We have scheduled a target-of-opportunity observation with the Follow-up X-ray Telescope (FXT) on board EP. Further follow-up observations are encouraged.

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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