{
  "eventId": "GRB 251222A",
  "body": "N. Pankov (HSE, IKI), V. Rumyantsev (CrAO), A. Pozanenko (IKI), A. Volnova (IKI) report on behalf of IKI-GRB-FuN:\n\nWe performed optical observations of 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 BVRI filters using the 2.6-meter ZTSh telescope of CrAO. The observations began in the I-filter on 2025-12-22 at 21:15 UT, i.e. 0.173 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) is detected in the majority of individual V,R images. \n\nThe observation properties and the preliminary photometry of a V,R-filter image pair are presented in the table below:\n\nDate       UT start  t-T0         Exp.    Filter   OT        Err.   UL\n                     (mid, days)  (s)                               (3sigma)\n2025-12-22 21:36:41  0.188142     120     V        19.14     0.08   20.8\n2025-12-22 21:38:48  0.189615     120     R        18.77     0.04   21.4\n\nThe photometry was calibrated using nearby stars from USNO-B1.0 and not corrected for the Galactic extinction. A power law fit to the R-filter light curve gives a temporal index of -0.64 +- 0.08.",
  "circularId": 43226,
  "submittedHow": "web",
  "bibcode": "2025GCN.43226....1P",
  "submitter": "Nicolai Pankov at IKI <colinsergesen@gmail.com>",
  "createdOn": 1766566631295,
  "format": "text/plain",
  "subject": "GRB 251222A: ZTSH BVRI optical observations"
}