TITLE:   GCN CIRCULAR
NUMBER:  43012
SUBJECT: GRB 251205A: Zeiss-1000 Koshka observatory optical observations
DATE:    25/12/06 14:44:43 GMT
FROM:    Alexei Pozanenko at IKI, Moscow <grb.alex@gmail.com>

N. Pankov (HSE,IKI), A. Novichonok (Petrozavodsk State University,
KIAM), S. Schmalz (KIAM), A. Volnova (IKI), A. Pozanenko (IKI) report
on behalf of IKI GRB-FuN:

We observed the optical afterglow of GRB 251205A (Lanava et al., GCN
43005; Lipunov et al., GCN 43006; de Ugarte Postigo et al., GCN 43008;
Malesani et al., GCN 43009; O'Neill et al., GCN 43010) using the
Zeiss-1000 telescope at Koshka observatory (INASAN). The observations
started/ended on 2025-12-06 (UT) 00:57:28/04:07:07. Preliminary
photometry of the initial stacked image is the following

Date UT start t-T0 Exp. Filter OT Err. UL(3sigma)
(mid, days) (s)

2025-12-06 00:57:28 0.05747 10*90 R  17.92 0.06 20.5

The photometry is based on nearby USNO-B1.0 stars and not corrected
for Galaxy extinction.