TITLE: GCN CIRCULAR NUMBER: 43207 SUBJECT: GRB 251222A: 1.3m DFOT optical detection DATE: 25/12/23 07:11:28 GMT FROM: ANSHIKA GUPTA at ARIES <anshika05180@gmail.com> Anshika Gupta, Kuntal Misra, Samrat Ghosh, Pankaj Pawar, Debalina Kar, and Dhruv Jain (ARIES) report: We observed the field of GRB 251222A detected by Fermi/GBM (Fermi GBM team, GCN 43186) and SVOM (Yang et al. 2025, GCN 43188) 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 2025-12-22 at 20:28:35 UT, i.e., ~ 3.38 hours after the Fermi/GBM trigger. We have taken multiple frames with an exposure time of 300s in the R filter. We stacked the images after the alignment. We detect an optical afterglow in our stacked image within the error box of SVOM (Palmerio et al. 2025, GCN 43189). We obtain the following preliminary magnitude in the stacked image: Date Start_UT T_start-T0 (hour) Filter Exp time (s) Magnitude =============================================================== 2025-12-22 20:28:35 ~3.38 R 300s*5 18.39 +/-0.01 The optical detection of the burst is consistent with Palmerio et al. 2025 (GCN 43189); An et al. 2025 (GCN 43194); Calapai et al. 2025 (GCN 43195); Durbak et al. 2025 (GCN 43197); Li et al. 2025 (GCN 43203); Saccardi et al. 2025 (GCN 43204). 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-B1.0 catalogue. View this GCN Circular online at https://gcn.nasa.gov/circulars/43207. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...