TITLE: GCN CIRCULAR NUMBER: 42998 SUBJECT: GRB 251203C: SVOM/COLIBRÍ (FM-GFT) optical upper limit DATE: 25/12/05 11:31:43 GMT FROM: nikos.mandarakas@lam.fr Nikos Mandarakas (LAM), Alan M. Watson (UNAM), Fredd Sanchez Alvarez (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), 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), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), M. Brunet (IRAP), N. A. Webb (IRAP): We imaged the field of the SVOM GRB 251203C (Brunet et al., GCN 42976) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-12-05T04:55:27 to 2025-12-05T06:22:35 UTC (from 34.36 to 35.81 hours after the trigger) and obtained 3840 seconds of exposure in the r and z filters. The data were reduced, coadded, and analyzed with the COLIBRÍ pipeline. The photometry was calibrated using nearby stars from the Pan-STARRS-DR1 catalog, is in the AB system, and was not corrected for Galactic extinction. In the stacked image, we no longer detect the optical counterpart reported by H.L. Li (GCN Circ. 42987) and D. Turpin et al. (CGN Circ. 42988), down to the following 3σ limit: r > 22.91 z > 22.47 We do detect a nearby extended source with coordinates RA = 51.782, Dec = -7.31, which is also seen in the Pan-STARRS-DR1 catalog, and could potentially correspond to the host of the GRB. The magnitudes we detect are: r = 22.34 +/- 0.14 z = 21.96 +/- 0.14 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/42998. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...