TITLE: GCN CIRCULAR NUMBER: 42500 SUBJECT: GRB251025B: 3.6m DOT Optical Observations DATE: 25/10/28 07:35:28 GMT FROM: ANSHIKA GUPTA at ARIES <anshika05180@gmail.com> Anshika Gupta, Kumar Pranshu, Dhruv Jain, Debolina Kar, Pankaj Pawar, and Kuntal Misra (ARIES) report: We observed the field of GRB 251025B detected by SVOM/ECLAIRs (Hussein et al. 2025; GCN 42437) with the 3.6m Devasthal Optical Telescope (DOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations were started on 2025-10-27 at 04:20:49.73 UT, i.e., ~1.58 days after the SVOM 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 counterpart in our stacked image within the error box of SVOM telescope (Hussein et al. 2025; GCN 42437) and Swift-XRT (Beardmore et al. 2025; GCN 42445). We obtain the following preliminary magnitude in the stacked image: Date Start_UT T_start-T0 (days) Filter Exp time (s) Magnitude ================================================================== 2025-10-27 04:20:49.73 ~1.58 ~ R 300s*8 20.866 +/-0.007 Our detection is consistent with Wu et al. 2025 (GCN 42438); Gress et al. 2025 (GCN 42439); Wu et al. 2025 (GCN 42440); Beardmore et al. 2025 (GCN 42445); Mohan et al. 2025 (GCN 42447); Hernández Fung et al. 2025 (GCN 42450); Pereyra et al. 2025 (GCN 42452); Li et al. 2025 (GCN 42453); Mo et al. 2025 (GCN 42459); Rakotondrainibe et al. 2025 (GCN 42460); Rajabov et al. 2025 (GCN 42466); Saccardi et al. 2025 (GCN 42472); Freeberg et al. 2025 (GCN 42474); Volnova et al. 2025 (GCN 42475). 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 catalog. View this GCN Circular online at https://gcn.nasa.gov/circulars/42500. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...