TITLE: GCN CIRCULAR NUMBER: 43566 SUBJECT: GRB 260128B: SVOM/COLIBRÍ (FM-GFT) optical upper limits DATE: 26/01/30 05:14:51 GMT FROM: enriquemm@astro.unam.mx Enrique Moreno Méndez (UNAM), Jean-Luc Atteia (IRAP), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), 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), Asuka Kuwata (UNAM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), N. A. Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), and Sébastien Le Stum (APC) report: We imaged the field of the SVOM GRB 260128A (Brunet et al., GCN Circ. 43561) using the DDRAGO two-channel wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2026-01-30 02:15 to 03:38 UTC (from 43.5 to 44.8 hours after the trigger) and obtained 60 minutes of simultaneous exposure in the r and z filters. The data were reduced, coadded, calibrated, and analyzed with the COLIBRÍ 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. WIthin the ECLAIRs 12 arcmin error circle (Brunet et al., GCN Circ. 43561), and in comparison to the corresponding PS1 images, we do not detect any new sources to preliminary 5-sigma limiting magnitudes of r > 22.3 z > 21.5 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/43566. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...