TITLE: GCN CIRCULAR NUMBER: 43424 SUBJECT: EP260116a: Einstein Probe detection of an X-ray transient DATE: 26/01/16 12:01:43 GMT FROM: EP Team at NAOC/CAS <ep_ta@bao.ac.cn> C. Wang, Z. X. Li, G. L. Huang, J. Y. Cao (IHEP), Y. H. Jiang (NJU), 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 EP260116a. A significant outburst is observed in the WXT light curve. The transient triggered EP-WXT (ID: 01709251336) at 2026-01-16T00:08:51 (UTC). The WXT position of the source is R.A. = 113.768 deg, DEC = 6.329 deg (J2000) with an uncertainty of 3 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 hydrogen column density of 7.65 x 10^20 cm^-2 and a photon index of 1.77. The derived average unabsorbed 0.5-4 keV flux is 7.16 x 10^-11 erg/s/cm^2. A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically with a 24-minute delay, starting at 2026-01-16 00:32:38 (UTC), by which time the outburst had already ended. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 113.7617 deg, DEC = 6.3244 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). The average FXT 0.5 - 10.0 keV spectra can also be fitted with an absorbed power law with the same hydrogen column density and a photon index of 1.98. The derived average unabsorbed 0.5-10.0 keV flux is 9.52 x 10^-14 erg/s/cm^2. 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/43424. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...