TITLE: GCN CIRCULAR NUMBER: 42434 SUBJECT: GRB 251025A: SVOM/COLIBRÍ (FM-GFT) optical upper limit DATE: 25/10/25 11:45:44 GMT FROM: nikos.mandarakas@lam.fr Nikos Mandarakas (LAM), Margarita Pereyra (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Fredd Alvarez (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), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), Z.M. Wang (BNU), W.J. Tan (IHEP): We imaged the field of the SVOM GRB 251025A (Wang et al., GCN Circ. 42432) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-10-25 09:58 to 11:00 UTC (from 0.39 to 1.41 hours after the trigger) and obtained 47 minutes of simultaneous exposure in the r and z filters. The data were analyzed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked images, we do not detect any new source within the MXT localization region (Wang et al., GCN Circ. 42432) down to the following 5-sigma limits: r > 22.9 z > 21.7 These upper limits are consistent with the one reported by Wu et al. (GCN Circ. 42433). 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/42434. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...