TITLE: GCN CIRCULAR NUMBER: 44911 SUBJECT: GRB 260610B / AT 2026owq: COLIBRÍ optical observations DATE: 26/06/11 11:14:07 GMT FROM: Dalya Akl at New York University Abu Dhabi <dka2010@nyu.edu> GRB 260610B / AT 2026owq: COLIBRÍ optical observations Dalya Akl (NYUAD), Enrique Moreno Méndez (UNAM), Jean-Grégoire Ducoin (CPPM), Rosa L. Becerra (UNAM), Noémie Globus (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of GOTO26fua/AT2026owq (O'Neill et al., GCN Circ. 44904), a possible counterpart of the Fermi GBM GRB 260610B (Fermi GBM team, GCN Circ. 44901), using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-06-11 06:51 to 08:13 UTC (from 7.08 to 8.45 hours after the GRB trigger) and obtained 15, 16, 15, 16, and 30 minutes, respectively, of exposure in the g, r, i, z, and y filters. The data were reduced, coadded, calibrated, and analysed with the COLIBRÍ pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR2 catalog, is in the AB system, and is not corrected for Galactic extinction. We detect the source AT2026owq with preliminary magnitudes of: g = 19.48 +/- 0.10 r = 19.02 +/- 0.03 i = 18.61 +/- 0.11 z = 18.54 +/- 0.08 y = 18.25 +/- 0.28 The absence of a strong break within our five filter measurements suggests a low-redshift event. Given the brightness, we encourage spectroscopic observations. Our values are consistent with those reported by GOTO (O'Neill et al., GCN Circ. 44903) and DDOTI (Watson et al., GCN Circ. 44905), given that the source continues to exhibit the same temporal decay reported by Watson et al. (GCN Circ. 44905), with a decay index of alpha ≈ -0.6. 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 México (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, México. View this GCN Circular online at https://gcn.nasa.gov/circulars/44911. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...