TITLE: GCN CIRCULAR NUMBER: 41573 SUBJECT: EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations DATE: 25/08/28 08:20:52 GMT FROM: EP Team at NAOC/CAS <ep_ta@bao.ac.cn> K. R. Ni (CCNU), Y. L. Hua (PMO,CAS), M. J. Liu and C. C. Jin (NAO,CAS) on behalf of the Einstein Probe (EP) team: The X-ray transient EP250827a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Hua et al., GCN 41553). We report on the refined analysis of WXT and FXT observations. The WXT data shows that the event started at T0=2025-08-27T07:39:01 (UTC) and lasted for at least 90 s. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 1.19 x 10^20 cm^-2 and a photon index of 0.73 (-0.47/+0.50). The derived average unabsorbed 0.5-4 keV flux is 1.71(-0.34/+0.42) x 10^(-9) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously about 102 s after T0. On-ground analysis of the FXT data found an uncatalogued source at R.A. = 3.46915, DEC = -56.4998 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), within the WXT error circle. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 1.19 x 10^20 cm^-2 and a photon index of 2.0(-0.10/+0.10). The derived average unabsorbed 0.5-10 keV flux is 4.38 (-0.38/+0.39) x 10^(-12)erg/s/cm^2. The uncertainties are at the 90% confidence level for the above 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). View this GCN Circular online at https://gcn.nasa.gov/circulars/41573. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...