TITLE: GCN CIRCULAR NUMBER: 42880 SUBJECT: GRB 251129A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate DATE: 25/11/29 03:38:10 GMT FROM: Camila Angulo Valdez at UNAM <camiangulo@astro.unam.mx> Camila Angulo (UNAM), Nikos Mandarakas (LAM), 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), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), N. A. Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), Wenjun Tan (IHEP), Defeng Kong (GXU), Wenjin Xie (NAOC), Donghua Zhao (NAOC), Hatsune Goto (Kanazawa Univ.) report: We imaged the field of the SVOM GRB 251129A (Tan et al., GCN Circ. 42877) using the DDRAGO two-channel wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-11-29 02:51:22 to 02:57:11 UTC (from 20.0 to 25.8 minutes after the trigger) and obtained 5 minutes of simultaneous exposure in the r and z filters. The data were reduced, coadded, 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 detect an uncatalogued source just outside the MXT error circle at: RA(J2000) = 14:57:18.88 = 224.2949 degrees Dec(J2000) = +79:17:34.8= 79.3050 degrees with an uncertainty of 0.5 arcsec. The preliminary magnitude derived for that source is: r = 18.30 +/- 0.01 z = 18.03 +/- 0.01 Further observations are ongoing. 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/42880. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...