TITLE: GCN CIRCULAR NUMBER: 43557 SUBJECT: GRB 260127A: INASAN-Kislovodsk, SAO RAS, and Terskol K-800 optical observations DATE: 26/01/29 15:04:48 GMT FROM: Alina Volnova at IKI RAS <alinusss@gmail.com> A. Volnova (IKI), A. Moskvitin (SAO RAS), N. Pankov (IKI), A. Tarasenkov (INASAN), I. Sokolov (INASAN, KIAM), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN collaboration: We observed the field of the Swift/Fermi/GBM GRB 260127A (Fermi GBM Team, GCN Circ. 43528; Klingler et al., GCN Circ. 43529; Osborne et al., GCN 43535; D'Ai et al, GCN 43539; Trigg, GCN 43546) in R-band with the RC500 telescope of the INASAN-Kislovodsk observatory starting on 2026-01-27 (UT) 23:20:50, in Rc-band with the Zeiss-1000 of the SAO RAS starting on 2026-01-28 (UT) 01:01:40, and in clear light with the 0.8-meter K-800 telescope of the Terskol observatory of INASAN 2026-01-28 (UT) 01:46:18. The optical counterpart reported previously (Saccardi & Malesani, GCN 43530; Lipunov et al., GCNs 43531, 43548; Wu et al., GCN 43537; Hagio et al., GCN 43540; Malesani et al, GCN 43543; Magnani et al., GCN 43544) is clearly detected in the stacked frame of the Zeiss-1000 and is not detected in the stacked frames of the RC500 and K-800 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) 2026-01-27 23:20:50 0.30822 110*120 R n/d n/d 21.9 INASAN-Kislovodsk/RC500 2026-01-28 01:01:40 0.32599 15*300 Rc 22.00 0.22 22.7 SAO RAS/Zeiss-1000 2026-01-28 01:46:18 0.35748 94*30 Clear n/d n/d 21.2 Terskol/K800 The photometry is based on several nearby stars from the USNO-B1 catalogue (R2 magnitudes) and is not corrected for the Galactic extinction. We would like to thank the SAO RAS engineering team: Afanasieva I. V., Pritychenko M. A., Egorov V. A., Shaldyrvan I. V. for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/43557. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...