TITLE: GCN CIRCULAR NUMBER: 44928 SUBJECT: EP260605a: COLIBRÍ optical upper limits DATE: 26/06/12 19:15:05 GMT FROM: Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra@astro.unam.mx> Rosa L. Becerra (UNAM), Massimiliano Lincetto (CPPM), Asuka Kuwata (UNAM), Sarah Antier (IJCLAB), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), 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), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), and Alan M. Watson (UNAM) report: We imaged the field of the EP260605a (Li et al., GCN Circ. 44847) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-06-06 07:27 to 08:05 UTC (from 21.93 to 22.59 hours after the trigger) and obtained 29 minutes of simultaneous exposure in the r and z filters. Given the proximity of the localization region to the Galactic bulge, we obtained additional observations to serve as templates. The field was reimaged on 2026-06-12 from 07:06 to 08:06 UTC (from 6.90 to 6.94 days after the trigger), yielding 42 minutes of simultaneous exposure in the r and z filters. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the SkyMapper catalog, is in the AB system, and is not corrected for Galactic extinction. In the image subtraction, we do not detect any new source within the FXT error region (Li et al., GCN Circ. 44867) down to the following 5-sigma limit: r > 21.4 z > 20.6 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/44928. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...