TITLE: GCN CIRCULAR NUMBER: 45049 SUBJECT: EP260526a: COLIBRÍ optical upper limit DATE: 26/06/27 10:31:22 GMT FROM: F. Magnani at Aix-Marseille Université, CPPM/CNRS <francesco.magnani.work@gmail.com> Francesco Magnani (CPPM), Fredd Sánchez Álvarez (UNAM), Jean-Grégoire Ducoin (CPPM), 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), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), and Alan M. Watson (UNAM) report: We imaged the field of the EP 260526a (J.P. Chen et al., GCN Circ. 45047) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-06-27T07:56:30 to 09:19:26 UTC (from 26.5 to 27.9 hours after the trigger) and obtained 64 minutes of simultaneous exposure in the r, z filters. The data were reduced, coadded, and analysed with the COLIBRÍ 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. In the stacked image, we do not detect any new source at the WXT source position (J.P. Chen et al., GCN Circ. 45047) down to the following 3-sigma limit: r > 23.87 z > 23.15 This upper limit is consistent with the one reported by R. A. J. Eyles-Ferris et al., GCN Circ. 45048. 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/45049. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...