TITLE: GCN CIRCULAR NUMBER: 44509 SUBJECT: GRB 260509A: SVOM/COLIBRÍ (FM-GFT) observations DATE: 26/05/10 04:54:27 GMT FROM: freddalvarez@astro.unam.mx Fredd Sánchez Álvarez (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), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM),Nikos Mandarakas (LAM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), and D. Adrien (CEA/Irfu) report: We imaged the field of the SVOM/ECLAIRs GRB 260509A (Götz et al. GCN 44504) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-10 03:31 to 03:59 UTC and obtained 8 minutes of exposure in g, r, and i, and simultaneously 24 minutes of exposure in z. The data were reduced, coadded, calibrated, and analyzed with the COLIBRÍ ASU 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 detect the optical counterpart reported by O’Neill et al.(GCN 44505), Saccardi et al. (GCN 44506), and Wu et al. (GCN 44507) with preliminary magnitudes of: g = 21.25 +/- 0.05 r = 21.31 +/- 0.08 i = 20.97 +/- 0.08 z = 20.81 +/- 0.09 Our strong detection of the source in g suggests that the redshift is less than 3.0. 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/44509. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...