TITLE: GCN CIRCULAR NUMBER: 45244 SUBJECT: EP260727a:refined analysis of the EP-WXT and EP-FXT observation DATE: 26/07/28 15:59:03 GMT FROM: EP Team at NAOC/CAS <ep_ta@bao.ac.cn> T. Wu, H. C. Ding (AHNU), J. W. Hu, Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP260727a triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Hu et al., GCN 45235) and followed by several optical telescopes (He et al., GCN 45234; Maksut et al., GCN 45238; Eyles-Ferris et al., GCN 45239; Adami et al., GCN 45243) with z_phot = 1.03 +/- 0.24 (He et al., GCN 45234). The refined analysis of the WXT data shows that the event started at T0=2026-07-27T20:36:47Z (UTC) and lasted for about 70 s before the observation was interrupted by the autonomous follow-up observation. The average WXT 0.5–4 keV spectrum can be fitted with an absorbed power-law model (tbabs*ztbabs*powerlaw) with a fixed Galactic hydrogen column density of 4.76 × 10^20 cm^-2 and a fixed redshift of z = 1.03. The best-fit photon index is 0.5 (-0.6/+1.2), and the intrinsic hydrogen column density is 7.1 (-7.1/+240.0) × 10^20 cm^-2. The derived average unabsorbed 0.5–4 keV flux is 1.8 (-0.5/+0.8) × 10^-9 erg/s/cm^2, corresponding to a luminosity of 3.0 (-0.8/+1.3) × 10^48 erg/s. The autonomous observation by the Follow-up X-ray Telescope (FXT) was performed at 2026-07-27T21:26:27 (UTC), about 50 minutes after T0. The exposure time of this observation is 2568 s. The on-ground analysis shows that an uncatalogued source was detected at R.A., Dec. = 346.4612, 3.1939 deg (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic). The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic equivalent hydrogen column density of 4.76 × 10^20 cm^-2 and a photon index of 2.0 (-0.6/+1.1), and the intrinsic hydrogen column density is 0.15 (-0.15/+0.87)×10^22 cm^-2. The derived average unabsorbed 0.5-10 keV flux is 4.4 (-2.7/+0.2)×10^-13 erg/s/cm^2, corresponding to a luminosity of 3.0 (-1.8/+0.11) × 10^45 erg/s. 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/45244. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...