TITLE: GCN CIRCULAR NUMBER: 41625 SUBJECT: EP250831a: EP-FXT follow-up observation DATE: 25/09/01 07:35:09 GMT FROM: EP Team at NAOC/CAS <ep_ta@bao.ac.cn> J. Yang (ZZU), X. Tian (GXU), D. Y. Li, Y. Liu (NAO, CAS) report on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of EP250831a (GCN 41619) at 2025-08-31T15:30:41 (UTC), about 6 hours after the WXT detection, with an exposure time of 2.9 ks. The source was also followed by Swift-XRT (GCN 41624). FXT detected an uncatalogued source within the WXT error circle at R.A. = 42.9816, DEC = -36.1872 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The FXT X-ray spectrum of this uncatalogued source can be fitted with an absorbed powerlaw with the absorption fixed at the Galactic value of 1.9x10^20 cm^-2, and a photon index of 1.4(-0.8, +0.8). The derived unabsorbed 0.5-10 keV flux is approximately 1.84x10^-13 erg/s/cm2. The uncertainties are at the 90% confidence level for the above parameters. We noted that EP-FXT also detected the uncatalogued X-ray source outside the WXT error circle detected by Swift-XRT. 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). View this GCN Circular online at https://gcn.nasa.gov/circulars/41625. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...