TITLE: GCN CIRCULAR NUMBER: 43632 SUBJECT: GRB 260131A/B: Mondy and Terskol optical observations DATE: 26/02/07 15:36:31 GMT FROM: Alina Volnova at IKI RAS <alinusss@gmail.com> A. Volnova (IKI), E. Klunko (ISTP), I. Sokolov (INASAN, KIAM), N. Pankov (IKI), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN: We observed the field of GRB 260131A/B (Fermi GBM Team, GCN 43579; Sugai et al., GCN 43580; Roberts et al., GCN 43585; Frederiks et al., GCN 43590; Luo et al., GCN 43591; Jiang et al., GCN 43600; Li et al., GCN 43605) with the AZT-33IK 1.5m telescope of the Mondy observatory on Feb. 4 and 5, and with the 2-meter Zeiss-2000 telescope of the Terskol observatory on Feb. 4 taking several frames in the R band. The optical counterpart reported by Gompertz et al., GCN 43586; Lee et al., GCN 43587; Saccardi et al., GCN 43595; García García et al., GCN 43599, Shi et al., GCN 43601; Sanchez-Ramirez et al., GCN 43604; Jayaraman et al., GCN 43606; Zhu et al., GCN 43607; Zheng et al., GCN 43609; Adami et al., GCN 43610, is detected in the stacked frame of every epoch. Preliminary photometry and observation data are the following: Date UT start t-T0 Exp. Filter Obj. Err. UL Site/Telescope (mid,days) (n*s) (3sigma) 2026-02-04 12:10:33 4.26118 43*120 R 19.56 0.04 22.3 Mondy/AZT-33IK 2026-02-04 15:54:04 4.41278 30*150 R 19.87 0.07 22.2 Zeiss-2000/Terskol 2026-02-05 13:40:24 5.32702 49*120 R 19.83 0.04 22.5 Mondy/AZT-33IK 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/43632. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...