TITLE: GCN CIRCULAR NUMBER: 45102 SUBJECT: GRB 260704A: SVOM/COLIBRÍ (FM-GFT) possible optical counterpart candidate DATE: 26/07/07 13:16:54 GMT FROM: F. Magnani at Aix-Marseille Université, CPPM/CNRS <francesco.magnani.work@gmail.com> GRB 260704A: SVOM/COLIBRÍ (FM-GFT) possible optical counterpart candidate Noémie Globus (UNAM), Francesco Magnani (CPPM), Camila Angulo (UNAM), Jean-Grégoire Ducoin (CPPM), Nathaniel R. Butler (ASU), Stéphane Basa (UAR Pytheas), Jean-Luc Atteia (IRAP), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García-García (UNAM), Ramandeep Gill (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), Alan M. Watson (UNAM), W.J Xie (NAOC), Y. H. Cheng (YNU), C. Plasse (HKU), report: We imaged the field of the SVOM GRB 260704A (W.J Xie et al., GCN Circ. 45072) using the DDRAGO two-channel wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2026-07-05 07:25:02 to 11:20:12 UTC (from 27.7 to 31.7 hours after the trigger) and obtained 104 minutes of simultaneous exposure in the r and z filters. The data were reduced, coadded, and analyzed with the 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 tentatively detected a faint, uncatalogued source consistent with both the SVOM/MXT error circle (W.J. Xie et al., GCN Circ. 45072) and the EP/FXT error circle (Y.-H. I. Yin et al., GCN Circ. 45078) at: RA (J2000) = 21:14:51.52 = 318.71468 deg, Dec (J2000) = -25:30:29.4 = -25.50816 deg, with an estimated astrometric uncertainty of 0.5 arcsec. The preliminary unsubtracted magnitude derived for that source was: r = 23.54 ± 0.22 z = 22.70 ± 0.27 We reobserved from 2026-07-06 07:18:26 to 09:47:39 UTC (from 51.62 to 54.11 hours after the trigger) and obtained 111 minutes of simultaneous exposure in the r and z filters. Compared to our previous observations, the source has faded. The preliminary unsubtracted magnitude is: r = 24.08 ± 0.23 mag, z = 23.19 ± 0.28 mag. The detection of the source in two independent optical bands, together with its fading between the two observing epochs, makes it a possible candidate for the optical counterpart of the GRB. 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/45102. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...