TITLE: GCN CIRCULAR NUMBER: 43869 SUBJECT: EP260227a: Einstein Probe detection of an X-ray transient and refined analysis DATE: 26/02/28 04:28:28 GMT FROM: EP Team at NAOC/CAS <ep_ta@bao.ac.cn> Y. Wang (PMO), H. C. Ding, T, Wu, Y. J. Yi (BNU), W. F. Wen (SZTU), Z. X. Ling(NAOC) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260227a. The transient triggered EP-WXT (ID: 01709258681) at 2026-02-27T20:12:29 (UTC). The WXT position of the source is R.A. = 223.101 deg, DEC = -11.408 deg (J2000) with an uncertainty of 2.586 arcmin in radius (90% C.L. statistical and systematic). The refined analysis of the WXT data shows that the event started at T0=2026-02-27T19:58:52 (UTC), and lasted for approximately 250 seconds. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 9.3×10^20 cm^-2 and a photon index of 0.8 (-0.6/+0.6). The derived average unabsorbed 0.5-4 keV flux is 4.1 (-1.3/+1.7) × 10^(-10) erg/s/cm^2. A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 223.1002 deg, DEC = -11.386 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic). The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 1.8 (-0.1/+0.1) × 10^21 cm^-2, and a photon index of 1.5 (-0.3/+0.3). The derived average unabsorbed 0.5-10 keV flux is 8.3 (-0.9/+1.2) ×10^(-12) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. The optical counterpart was reported by Eyles-Ferris et al. (GCN 43867) and Li et al. (GCN 43868). 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/43869. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...