GCN 43557: GRB 260127A: INASAN-Kislovodsk, SAO RAS, and Terskol K-800 optical observations

2026-01-29T15:04:48.207Z | rev 0 | event: GRB 260127A
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.