TITLE: GCN CIRCULAR NUMBER: 43668 SUBJECT: GRB 260208B: COLIBRÍ optical observations DATE: 26/02/09 13:16:57 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), 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), 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 bright Fermi GRB 260208B (Fermi GBM Team, GCN Circ. 43638), also detected by SVOM/GRM (L. Xing-Hao, GCN Circ. 43650), using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-02-09T05:10:25 to 2026-02-09T06:30:45 UTC (from 19.3 to 20.6 hours after the trigger) and obtained 30 minutes of simultaneous exposure in the r, 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 PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. We detect a source at the position of the SVOM/VT candidate (Li et al., GCN Circ. 43659), with the following preliminary magnitudes : r = 22.61 +/- 0.14 z = 21.99 +/- 0.25 Further analysis 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/43668. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...