TITLE: GCN CIRCULAR NUMBER: 43100 SUBJECT: GRB 251214B: 1.3m DFOT optical detection DATE: 25/12/14 20:36:58 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 251214B detected by Fermi/GBM (Fermi GBM team, GCN 43088) and Swift/BAT (Eyles-Ferris et al. 2025, GCN 43089) 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 2025-12-14 at 12:59:37 UT, i.e., ~ 3.95 hours after the Fermi/GBM 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 an optical afterglow in our stacked image within the error box of Swift/UVOT (Eyles-Ferris et al. 2025, GCN 43089). We obtain the following preliminary magnitude in the stacked image:

Date Start_UT T_start-T0 (hour) Filter Exp time (s) Magnitude =============================================================== 2025-12-14 12:59:37 ~3.95 I 300s*18 20.03 +/-0.03

The optical detection of the burst is consistent with Eyles-Ferris et al. 2025 (GCN 43089); Lipunov et al. 2025 (GCN 43091); Kang et al. 2025 (GCN 43093); Gress et al. 2025 (GCN 43095); and Fu et al. 2025 (GCN 43097).

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/43100. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...