TITLE: GCN CIRCULAR NUMBER: 44417 SUBJECT: GRB 260424B: COLIBRÍ optical upper limit DATE: 26/04/28 19:07:11 GMT FROM: Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra@astro.unam.mx> Massimiliano Lincetto (CPPM), Fredd Sánchez Álvarez (UNAM), Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of GRB 260424B (SVOM/GRM Team et al., GCN Circ. 44410; Kozyrev et al., GCN Circ. 44411; Fermi GBM Team GCN Circ. 44413; Ridnaia et al., GCN Circ. 44416) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-04-28 10:43 to 11:45 UTC (from 3.80 to 3.84 days after the trigger) and obtained 48 minutes of simultaneous exposure in the i/z filters. The data were reduced and coadded with COLIBRÍ ASU pipeline and analysed in 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 image, and after performing image subtraction against PanSTARRS DR1 templates, we do not detect any new source at the IPN region (Kozyrev et al., GCN Circ. 44411) down to the following 5-sigma limits: i > 22.6 z > 21.9 Our images also include the bright galaxy PSO J348.1125+41.2291, centered at RA, Dec = 348.1125, 41.2290, with reported magnitudes of g=17.03, r=16.25, i=15.90, and z=15.61. This galaxy is just outside the IPN region. However, in image-subtraction analysis, we find no evidence for any additional component in the galaxy. We thank Chenwei Wang (SVOM/GRM) for the helpful communication, and the IPN team for their rapid analysis and prompt release of a refined position, which facilitated the observations of the region. We thank the staff of the Observatorio Astronómico Nacional at Sierra de San Pedro Mártir, as well as the technical and engineering teams at CEA, CPPM, IRAP, LAM, OHP, OSU Pytheas, and UNAM. 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/44417. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...