TITLE: GCN CIRCULAR NUMBER: 45172 SUBJECT: GRB 260714B: COLIBRÍ optical counterpart candidate DATE: 26/07/16 06:56:58 GMT FROM: Rosa Leticia Becerra at Instituto de Astronomía, UNAM <rbecerra@astro.unam.mx> Rosa L. Becerra (UNAM), Stéphane Basa (UAR Pytheas), Jean-Grégoire Ducoin (CPPM), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), 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), 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), Antonio de Ugarte Postigo (LAM), and Alan M. Watson (UNAM) report: We imaged the field of the *Fermi* GRB 260714B (*Fermi* GBM Team GCN Circ. 45158; Mukherjee et al., GCN Circ. 45161; Gupta et al., GCN Circ. 45162) also detected by AstroSat CZTI (Sharma et al., GCN Circ. 45163) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-07-16 03:46 to 05:23 UTC (from 1.39 to 1.46 days after the trigger) and obtained 59 and 71 minutes of exposure in the r and z filters, respectively. The data were reduced, coadded and analysed with the ASU 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 detect an uncatalogued source, not present in the Legacy Survey catalog (Dey et al. 2019), located within the *Fermi*/GBM error circle (*Fermi* GBM Team, GCN Circ. 45158) at the following position: RA(J2000) = 10:52:58.41 = 163.2434 deg, Dec(J2000) = +46:49:20.0 = 46.8222 deg, with an uncertainty of 0.5 arcsec. The position is 10.7 arcmin from the center of the *Fermi*/LAT localization (Gupta et al., GCN Circ. 45162), placing it outside the reported *Fermi*/LAT error region (6.6 arcmin). The preliminary magnitudes derived for that source are: r = 21.47 +/- 0.04, z = 21.33 +/- 0.09. The brightness and red color of the source are, however, consistent with those commonly observed in GRB afterglows, making it a plausible candidate for the optical counterpart of GRB 260714B. Combined with the high-energy emission detected by *Fermi*/LAT and the E*peak* determined from the subsequent analysis of the *Fermi*/GBM team (Mukherjee et al., GCN Circ. 45161), these properties motivate further follow-up. We encourage photometric monitoring to establish whether the source is fading, as well as spectroscopic observations to determine its distance. 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/45172. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...