TITLE: GCN CIRCULAR NUMBER: 43273 SUBJECT: GRB 251222A: Mondy Optical Observations DATE: 25/12/30 17:23:31 GMT FROM: Nicolai Pankov at IKI <colinsergesen@gmail.com> N. Pankov (HSE, IKI), E. Klunko (ISTP), A. Pozanenko (IKI), A. Volnova (IKI) report on behalf of IKI-GRB-FuN: We observed the field of GRB 251222A (The Fermi GBM team, GCN 43186; Yang et. al, GCN 43188; Preis & Greiner, GCN 43190; Evans, GCN 43191; Beardmore et. al, GCN 43213; Frederiks et. al, GCN 43214; Guo et. al, GCN 43218; Neights et. al, GCN 43222) at z = 3.171 (Saccardi et. al, GCN 43204) in the R filter using the 1.5-meter AZT-33IK telescope of the Sayan Solar Observatory (Mondy). The observations began on 2025-12-25 at 14:32 UT, i.e. ~2.91 days since trigger. The optical counterpart (Palmerio et. al, GCN 43189; An et. al, GCN 43194; Calapai et. al, GCN 43195; Durbak et. al, GCN 43197; Li et. al, GCN 43203; Saccardi et. al, GCN 43208; Gupta et. al, GCN 43207; Saccardi et. al, GCN 43204; Kumar et. al, GCN 43209; Pérez-Fournon et. al, GCN 43212; Gupta et al., GCN 43224; Globus et al., GCN 43225; Freeberg et al., GCN 43229; Volnova et al., GCN 43230; Busmann et al., GCN 43233; Lee et al., GCN 43236; Maksut et al., GCN 43237; Kumar et al., GCN 43250) is detected in the co-add image of 30x120 sec. The observation details and preliminary photometry are presented in the table below: Date UT start t-T0 Exp. Filter OT Err. UL (mid, days) (s) (3sigma) 2025-12-25 14:32:35 2.91441 30*120 R 21.66 0.12 22.9 The photometry was calibrated using nearby stars from USNO-B1.0 and not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43273. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...