TITLE: GCN CIRCULAR NUMBER: 42870 SUBJECT: GRB 251126A: further SAO RAS optical observations DATE: 25/11/28 12:46:09 GMT FROM: Alexander Moskvitin at SAO RAS mosk@sao.ru

A. Moskvitin (SAO RAS), V. Goranskij (SAI MSU, SAO RAS), V. S. Shergin (SAO RAS), A. A. Volnova (IKI), A. S. Pozanenko (IKI) report on behalf of IKI-GRB-FuN and GRB follow-up team.

We observed the field of the Swift GRB 251126A (Caputo et al., GCN 42843; Evans, GCN 42845; Goad et al., GCN 42851; Page et al., GCN 42860) with the Zeiss-1000 1m telescope of the SAO RAS on November 27/28 night. We obtained two series of 300 sec. images in Rc band under a good weather conditions and seeing (FWHM) ~1".5.

The optical afterglow (Swain, GCN 42844; Fu et al., GCN 42848; Reguitti et al., GCN 42849; Broens et al., GCN 42850; Anguloet al., GCN 42855; Pulido-Torres et al; GCN 42856; Gupta et al., GCN 42857; Cotter et al., GCN 42858; Seki et al., GCN 42859; Volnova et al., GCN 42861; Breeveld and Caputo, GCN 42863; Gupta et al., GCN 42864; Burkhonov et al., GCN 42866; Maksut et al., GCN 42868) is clearly detected in the stacked frames. The preliminary results are as following.

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

2025-11-27 20:20:22 1.07076 11*300 Rc 22.02 0.04 24.1 2025-11-27 23:31:00 1.19809 8*300 Rc 22.24 0.07 23.8

The photometry is based on nearby stars from the USNO-B1 catalogue (R2 magnitudes)and is not corrected for the Galactic extinction.

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