TITLE: GCN CIRCULAR NUMBER: 43221 SUBJECT: EP251220a: CrAO ZTSh optical observations DATE: 25/12/23 18:19:15 GMT FROM: Alina Volnova at IKI RAS <alinusss@gmail.com> A. A. Volnova (IKI), V. V. Rumyantsev (CrAO), A. S. Pozanenko (IKI), N. S. Pankov (HSE, IKI) report on behalf of IKI-GRB-FuN: We observed the field of the fast X-ray transient EP251220a detected by EP/WXT (Liu et al., GCN 43162) with the ZTSh 2.6m telescope of CrAO taking several 120-second frames in R-band. The observations started on Dec. 22 at UT 20:32:36, i.e., ~ 2.5 days after the EP/WXT trigger. In the stacked image we detect the optical counterpart reported previously (Sánchez Álvarez et al., GCN 43167; Kumar et al., GCN 43169; Rakotondrainibe et al., GCN 43170; Busmann et al., GCN 43181; van Hoof et al., GCN 43182; An et al., GCN 43184; Passaleva et al., GCN 43185). Preliminary photometry and observational details are the following: Date UT start t-T0 Exp. Filter Obj. Err. UL Site/Telescope (mid,days) (n*s) (3sigma) 2025-12-22 20:32:36 2.51642 17*120 R 22.55 0.20 22.9 CrAO/ZTSh The photometry is based on several nearby stars from the USNO-B1 catalogue (R2 magnitudes) and is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43221. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...