TITLE: GCN CIRCULAR NUMBER: 40119 SUBJECT: GRB 250407A: EP-WXT afterglow detection DATE: 25/04/08 09:47:28 GMT FROM: EP Team at NAOC/CAS ep_ta@bao.ac.cn
T. C. Zheng, D. F. Hu (PMO, CAS), X. Mao, W. X. Wang, W. D. Zhang (NAO, CAS) report on behalf of the Einstein Probe team:
We report on the detection of the X-ray afterglow of GRB 250407A by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. In an observation starting at 2025-04-07T17:11:31.158 (UTC), WXT detected an uncatalogued X-ray source at a position R.A. = 110.767 deg, DEC = 36.800 deg (J2000) with an uncertainty of 2.7 arcmin (radius, 90% C.L. statistical and systematic). This source is only 25 arcsec away from the X-ray afterglow of GRB 250407A that was detected by Swift/XRT (GCN 40113). The WXT observation started about 83 minutes after the trigger of GRB 250407A by Fermi/GBM (GCN 40104). The temporal and spatial coincidence suggests that WXT likely detected the X-ray afterglow of GRB 250407A.
The observation lasted for 422 seconds, during which no significant variation was observed. The time-averaged spectrum can be fitted with an absorbed powerlaw model, with a photon index of 1.5(-0.7/+0.8), while nH is fixed at the Galactic value of 7.1 x 10^20 cm^-2. The unabsorbed 0.5-4 keV flux is estimated to be 2.0 (-0.7/+1.2) x 10^-10 erg/s/cm^2. The uncertainties are quoted at the 90% confidence level for the above spectral parameters.
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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