TITLE: GCN CIRCULAR NUMBER: 43330 SUBJECT: EP260104a: Einstein Probe detection of a fast X-ray transient DATE: 26/01/05 08:41:44 GMT FROM: EP Team at NAOC/CAS <ep_ta@bao.ac.cn> H. Zhou (PMO, CAS), Z. C. Zou (NJU), J. P. Chen (SYSU), Y. J. Yi (BNU), D. Y. Li, C. L. Guo, Z. X. Ling, Y. Liu (NAO, CAS) 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 EP260104a. The transient triggered EP-WXT (ID: 01709250979) at 2026-01-04T10:25:44 (UTC). The WXT position of the source is R.A. = 178.535 deg, DEC = 16.491 deg (J2000) with an uncertainty of 2.8 arcmin in radius (90% C.L. statistical and systematic). Since EP260104a was triggered in SAA region, no autonomous follow-up observation was performed. We analyzed the telemetry data, and the 0.5-4 keV rate light curve shows a single pulse lasting for about 150 seconds. The absorbed powerlaw model with a fixed Galactic column density of Hydrogen of 4.57 x 10^20 cm^-2 was adopted to fit the average WXT spectrum. The best-fitted photon index is 2.44(+1.26/-0.96), the average flux (0.5-4 keV) is (2.4+/-1.1) x 10^-10 erg s^-1 cm^-2, and no additional absorption is required. All uncertainties are reported in 90% C.L. We have arranged X-ray follow-up observations and will update the information upon receiving the data. 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/43330. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...