TITLE: GCN CIRCULAR NUMBER: 44978 SUBJECT: EP260618a: EP-WXT detection of an X-ray transient DATE: 26/06/18 15:21:15 GMT FROM: EP Team at NAOC/CAS <ep_ta@bao.ac.cn> J. Yang (ZZU), S. Q. Jiang (NAO, CAS), H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient, designated EP260618a, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission through the ground data analysis. The transient was detected in one WXT observation starting at 2026-06-18T08:34:46 (UTC). No significant variability was detected during the 2.7 ks exposure. The position of the transient is R.A. = 276.676 deg, Dec. = 23.849 deg (J2000), with an uncertainty radius of 2.5 arcmin (90% confidence level, including both statistical and systematic uncertainties). There is no historical X-ray source in the WXT error circle. The average 0.5-4 keV spectrum can be fitted by an absorbed power law with a fixed Galactic hydrogen column density of 1.32^21 cm^-2 and a photon index of 1.4 (-0.4/+0.5). The derived average unabsorbed 0.5-4 keV flux is 6.9 (-1.7/+2.1) x 10^(-11) erg cm^-2 s^-1. The position of EP260618a falls within the error circle of GRB 260618A reported by Fermi/GBM (GCN 44973), suggesting that EP260618a may be the X-ray afterglow of GRB 260618A. Follow-up observation with the Follow-up X-ray Telescope (FXT) onboard EP has been scheduled. Launched on 2024 January 9, Einstein Probe is a space-based X-ray observatory designed to monitor the dynamic X-ray sky and perform rapid follow-up observations of newly discovered transients (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/44978. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...