TITLE: GCN CIRCULAR NUMBER: 43225 SUBJECT: GRB 251222A: SVOM/COLIBRÍ (FM-GFT) optical observations DATE: 25/12/24 08:20:51 GMT FROM: globus@astro.unam.mx Noémie Globus (UNAM), Camila Angulo (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Nikos Mandarakas (LAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), and Hui Yang (IRAP) report: We imaged the field of GRB 251222A (Fermi GBM team, GCN Circ. 43186; Yang et al., GCN Circ. 43188; Guo et al., GCN Circ. 43201; Frederiks et al., GCN Circ. 43214; Guo et al. GCN Circ 43218) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-12-23 04:28 UTC to 08:22 UTC (from 11.37 to 15.27 hours after the trigger) and obtained 78 and 103 minutes of exposure in the r and z filters, respectively. We observed in poor weather conditions with variable transparency. The data were reduced, coadded, calibrated, and analyzed with the ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. We detected the optical counterpart discovered by Palmerio et al. (GCN Circ. 43189), and subsequently observed by An et al. (GCN Circ. 43194), Calapai (GCN Circ. 43195), Durbak et al. (GCN Circ, 43197), Li et al. (GCN Circ. 43203), Saccardi et al. (GCN Circ. 43204), Gupta et al. (GCN Cric. 43207), Saccardi et al. (GCN Circ. 43208), Kumar et al. (GCN Circ 43209), Pérez-Fournon et al. (GCN Circ. 43212) and Gupta et al. (GCN Circ. 43224), at preliminary magnitudes of: r = 19.83 +/- 0.01, z = 19.39 +/- 0.01. During our observations, the afterglow fades smoothly, with no evidence for further rebrightenings like the one reported by Li et al. (GCN Circ. 43203). We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/43225. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...