TITLE: GCN CIRCULAR NUMBER: 44530 SUBJECT: GRB 260510C: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate DATE: 26/05/11 06:35:13 GMT FROM: Camila Angulo Valdez at UNAM <camiangulo@astro.unam.mx> Camila Angulo (UNAM), Dalya Akl (NYUAD), Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Sarah Antier (IJCLAB), 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), Asuka Kuwata (UNAM), Massimiliano Lincetto (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) and Antonio de Ugarte Postigo (LAM) and Andrea Saccardi (CEA/Irfu ) report: We imaged the field of the SVOM/ECLAIRs and Fermi/GBM GRB 260510C (Fermi GBM Team, GCN Circ. 44520; Gotz et al., GCN Circ. 44521) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-11 04:46 to 05:39 UTC (from 11.54 to 12.44 hours after the trigger) and obtained 24 minutes of simultaneous exposure in r and z filters. 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 an uncatalogued source 1.06 arcmin away from the MXT position and slightly outside the 90% uncertainty region reported by SVOM, but still inside the ECLAIRs region (Gotz et al., GCN Circ. 44521), at: RA(J2000) = 10:31:45:49 = 157.9394 degrees Dec(J2000) = +02:50:15.5 = 2.83763 degrees with an uncertainty of 0.5 arcsec. The preliminary unsubtracted magnitudes derived for that source are: r = 21.32 + /- 0.03, z = 20.23 + /- 0.03. We suggest this is the optical counterpart of the GRB. The position of the candidate is consistent with a faint galaxy with reported magnitudes of g = 23.61 +/- 0.10, r = 23.49 +/- 0.14, i = 23.02 +/- 0.12 and z = 23.03 +/- 0.21 and a photo-z of =0.89 +/- 0.63 in the DESI Legacy Survey catalog (Dey et al. 2019), so our candidate is two magnitudes brighter than the galaxy. We suggest this galaxy may be the host. 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/44530. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...