TITLE: GCN CIRCULAR NUMBER: 43937 SUBJECT: EP260306a: refined analysis of the EP-WXT and EP-FXT observations DATE: 26/03/07 02:34:23 GMT FROM: EP Team at NAOC/CAS <ep_ta@bao.ac.cn> G.L. Huang, Z.X. Li (IHEP), H. Zhou (PMO, CAS) and Z.-X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP260306a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Huang et al., GCN 43930). The refined analysis of the WXT data shows that the event started at T0=2026-03-06T 01:28:20(UTC), and lasted for approximately 60 seconds, after which the WXT light curve was interrupted due to the autonomous follow-up observation. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density (NH) of 3.24×10^20 cm^-2, a photon index of 4.01(-2.04/+3.04) and an additional absorber (z=0) of NH=6.32(-4.37/+6.21)×10^21cm^-2 to represent the comprehensive absorption of the host galaxy (z=4.773, Levan et al., GCN 43934) and the foreground galaxy (z=0.72, Globus et al., GCN 43931). The derived average unabsorbed 0.5-4 keV flux is 3.98×(-2.97/+69.04)×10^(-9) erg/s/cm^2. The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously at 2026-03-06T01:34:41(UTC, T0+261s). The exposure time of this observation is 4010s. On-ground analysis of the FXT data found an uncatalogued source at R.A. = 145.9497, DEC = 15.6942 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), which is consistent with the WXT position and position of the optical counterpart (Li et al, GCN 43929; Globus et al., GCN 43931; Ma et al., GCN 43933; Levan et al., GCN 43934). The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 3.24×10^20 cm^-2, a photon index of 2.36(-0.38/+0.41) and an additional absorber of NH=1.53(-1.11/+1.19)×10^21 cm^-2. The derived average unabsorbed 0.5-10 keV flux is 1.37(-0.16/+0.20)×10^(-12) erg/s/cm^2. All uncertainties are reported at the 90% confidence interval. Further FXT follow-up observations have been arranged. 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/43937. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...