TITLE: GCN CIRCULAR NUMBER: 43520 SUBJECT: EP260126a: Einstein Probe detection of a fast X-ray transient DATE: 26/01/27 02:36:26 GMT FROM: EP Team at NAOC/CAS <ep_ta@bao.ac.cn> S.Y. Fu (HUST), Z.M. Wang (BNU), J.H. Wu (GZHU), H.Y. Liu, H.W. Pan (NAOC, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260126a. The event started at 2026-01-26T04:25:01 (UTC) and lasted for about 1400 seconds. The WXT position of the source is R.A. = 103.737 deg, DEC = 37.699 deg (J2000) with an uncertainty of 2.1 arcmin in radius (90% C.L. statistical and systematic).   The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a photon index of 1.16(-/+0.17) and with a fixed galactic hydrogen column density of 1.21 x 10^21 cm^-2. The derived average unabsorbed 0.5-4 keV flux is 2.77 (-0.26/+0.29) x 10^-10 erg/s/cm^2. The peak flux in the 0.5-4 keV band reaches 1.49(-0.14/+0.16) x 10^-9  erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed at 2026-01-26T23:08:05 (UTC), about 19 hours after the trigger. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 103.7537 deg, DEC = 37.7067 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). Further information will be updated when the telemetry data is received. 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/43520. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...