TITLE: GCN CIRCULAR NUMBER: 44991 SUBJECT: EP260618a: EP-FXT follow-up observation DATE: 26/06/19 09:13:11 GMT FROM: EP Team at NAOC/CAS <ep_ta@bao.ac.cn> S. Q. Jiang (NAO, CAS), J. Yang (ZZU), H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of the X-ray transient EP260618a (Yang et al., GCN 44978), which is possibly associated with GRB 260618A (Fermi GBM team, GCN 44973). The observation started at 2026-06-18T18:09:47 (UTC), about 9.58 hours after the initial WXT detection, with an exposure time of 3 ks. An uncatalogued source was detected within the WXT error circle at R.A. = 276.6799, DEC = 23.8439 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The FXT spectrum can be fitted with an absorbed powerlaw with a hydrogen column density fixed at the Galactic value of 1.32 x 10^21 cm^-2 and a photon index of 2.09 +/- 0.13. The derived unabsorbed 0.5-10 keV flux is 1.28 (+0.13, -0.10) x 10^-12 erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. The position of the uncatalogued X-ray source is consistent with the optical counterpart (Becerra et al., GCN 44988; Malesani et al., GCN 44990). Further EP-FXT follow-up observations will be arranged. 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/44991. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...