TITLE: GCN CIRCULAR NUMBER: 42107 SUBJECT: EP251003a: Einstein Probe detection of an X-ray transient DATE: 25/10/05 03:22:32 GMT FROM: EP Team at NAOC/CAS <ep_ta@bao.ac.cn> Q. C. Liu (THU), Y. Q. Zhao (USTC), C. Zhou (HUST), H. W. Pan (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 EP251003a. The WXT position of the source is R.A. = 56.934 deg, DEC = -10.929 deg (J2000) with an uncertainty of 2.549 arcmin in radius (90% C.L. statistical and systematic). The transient was first detected by WXT in an observation that started at 2025-10-03T18:11:50 (UTC). The 0.5-4 keV spectrum can be fitted with an absorbed powerlaw model with hydrogen column density of 0.4(+3.2, -0.4)x10^21 cm^-2 and a photon index of 0.9(+1.1, -0.5). The average unabsorbed 0.5-4 keV flux is 3.8(+1.4, -1.1) x 10^-11 erg/s/cm^2. A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed. An uncatalogued X-ray source was detected at R.A. = 56.9218 deg, DEC = -10.9321 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic). The 0.5-10 keV spectrum can be fitted with an absorbed powerlaw model with hydrogen column density of 0.0 (+1.7, -0.0)x10^21 cm^-2 and a photon index of 1.7(+0.6, -0.2). The average unabsorbed 0.5-10 keV flux is 8.3(+1.6, -1.9) x 10^-13 erg/s/cm^2. All the uncertainties of the parameters are 90% C.L. statistical. Further follow-up observations are encouraged. 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/42107. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...