TITLE: GCN CIRCULAR NUMBER: 43223 SUBJECT: EP251220a: 3.6m DOT optical afterglow detection DATE: 25/12/23 19:45:40 GMT FROM: ANSHIKA GUPTA at ARIES <anshika05180@gmail.com> Anshika Gupta, Kuntal Misra, Divyanshu Janghel, Debalina Kar, Dhruv Jain, and Pankaj Pawar (ARIES) report: We observed the field of EP251220a detected by EP/WXT (Liu et al. 2025; GCN 43162) 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 2025-12-21 at 17:13:18 UT, i.e., ~1.36 days after the EP/WXT 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 a optical counterpart in our stacked image within the error box of COLIBRÍ telescope (Sánchez Álvarez et al. 2025; GCN 43167). We obtain the following preliminary magnitude in the stacked image: Date Start_UT T_start-T0 (days) Filter Exp time (s) Magnitude ================================================================== 2025-12-21 17:13:18 ~1.36 r 300s*8 21.64 +/-0.02 Our detection is consistent with Lipunov et al. 2025 (GCN 43163); Sánchez Álvarez et al. 2025 (GCN 43167); Kumar et al. 2025 (GCN 43169); Rakotondrainibe et al. 2025 (GCN 43170); Busmann et al. 2025 (GCN 43181); van Hoof et al. 2025 (GCN 43182); An et al. 2025 (GCN 43184); Passaleva et al. 2025 (GCN 43185); Volnova et al. 2025 (GCN 43221). 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 PanSTARRS DR1 catalog. View this GCN Circular online at https://gcn.nasa.gov/circulars/43223. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...