TITLE: GCN CIRCULAR NUMBER: 42857 SUBJECT: GRB 251126A: 1.3m DFOT optical afterglow detection DATE: 25/11/27 08:14:19 GMT FROM: ANSHIKA GUPTA at ARIES <anshika05180@gmail.com> Anshika Gupta, Dhruv Jain, Pankaj Pawar, Debalina kar and Kuntal Misra (ARIES) report: We observed the field of GRB 251126A detected by Swift (Caputo et al. 2025, GCN 42843) with the 1.3m Devasthal Fast Optical Telescope (DFOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations were started on 2025-11-26 at 22:17:19 UT, i.e., ~3.11 hour after the Swift trigger. We have taken multiple frames with an exposure time of 300s in the I filter. We stacked the images after the alignment. We detect the optical counterpart in our stacked image within the error box of GIT (Swain et al. 2025, GCN 42844). We obtain the following preliminary magnitude in the stacked image: Date Start_UT T_start-T0 (hour) Filter Exp time (s) Magnitude ====================================================================== 2025-11-26 22:17:19 ~3.11 I 300*12 19.41+/- 0.01 Our detection is consistent with Swain et al. 2025 (GCN 42844); Lipunov et al. 2025 (GCN 42847); Fu et al. 2025 (GCN 42848); Reguitti et al. 2025 (GCN 42849); Broens et al. 2025 (GCN 42850); Angulo et al. 2025 (GCN 42855); and Torres et al. 2025 (GCN 42856). The magnitude is not corrected for the Galactic extinction in the direction of the burst. Photometric calibration is performed using the standard stars from the USNO-B1 catalog. View this GCN Circular online at https://gcn.nasa.gov/circulars/42857. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...