TITLE: GCN CIRCULAR NUMBER: 43771 SUBJECT: GRB 260208A: AbAO and Terskol optical upper limits DATE: 26/02/17 14:19:08 GMT FROM: Alina Volnova at IKI RAS <alinusss@gmail.com> A. Volnova (IKI), R. Ya. Inasaridze (AbAO), I. Sokolov (INASAN, KIAM), A. Pozanenko (IKI), N. Pankov (IKI) report on behalf of IKI-GRB-FuN: We observed the field of GRB 260208A (Fermi GBM team, GCN 43635; Sonawane et al. 2026, GCN 43642; Longo et al. 2026, GCN 43645; Dichiara et al. 2026, GCN 43652; Luo et al. 2026, GCN 43658; Mukherjee & Meegan, GCN 43673; Waratkar & Grefenstette, GCN 43674; Cheung et al., GCN 43675) at z = 2.36 (Dimple et al., GCN 43662) with the 0.7-meter AS-32 telescope of Abastumani Observatory (AbAO) and with the 2-meter Zeiss-2000 telescope of the Terskol observatory on Feb. 10 taking several R-filter exposures. We do not detect the optical counterpart (Lipunov et al., GCN 43640; Wortley et al., GCN 43641; Dichiara et al., GCN 43652; Ma et al., GCN 43655; Ahumada et al., GCN 43657; Dimple et al., GCN 43661; Magnani et al., GCN 43664; Gupta et al., GCN 43665; Volnova et al., GCN 43666, 43770; Pérez-Fournon et al., GCN 43694; Kuin & Cenko, GCN 43702) in the stacked frames of both telescopes. 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) 2026-02-10 21:58:14 2.77172 65*120 R n/d n/d 20.4 AbAO/AS-32 2026-02-10 23:52:31 2.81612 21*150 R n/d n/d 21.2 Terskol/Zeiss-2000 The photometry is based on nearby SDSS stars (R-magnitudes obtained using the 2005 Lupton transformation equations) and is not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43771. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...