TITLE: GCN CIRCULAR NUMBER: 43664 SUBJECT: GRB 260208A: COLIBRÍ optical observations DATE: 26/02/09 11:14:54 GMT FROM: F. Magnani at Aix-Marseille Université, CPPM/CNRS <francesco.magnani.work@gmail.com> Francesco Magnani (CPPM), Leonardo García García (UNAM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (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), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Asuka Kuwata (UNAM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Enrique Moreno Méndez (UNAM), 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 the Fermi GRB 260208A (43635, GCN Circ. 43642, Fermi LAT, GCN Circ. 43645, GECAM-B, GCN Circ. 43658) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. 2026-02-09T08:16:25.726 to 2026-02-09T09:37:56.715 UTC (from 27.15 to 28.51 hours after the trigger) and obtained 30 minutes of simultaneous exposure in the r, z filters. The data were reduced and 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. We detected the optical counterpart Lipunov et al. (GCN Circ. 43640), Wortley et al. (GCN Circ. 43641), Dichiara et al. (GCN Circ. 43652), Ma et al. (GCN Circ. 43655), Ahumada et al. (GCN Circ. 43657), Dimple et al. (GCN Circ. 43661), with measured redshift z = 2.36 (Dimple et al. GCN Circ. 43662) at a preliminary magnitude of: r = 21.09 +/- 0.04 z = 20.64 +/- 0.06 Further observations are ongoing. 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/43664. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...