TITLE: GCN CIRCULAR NUMBER: 43902 SUBJECT: GRB 260303A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate DATE: 26/03/03 07:31:10 GMT FROM: Benjamin Schneider at MIT <bschn@mit.edu> Benjamin Schneider (LAM), Rosa L. Becerra (UNAM), Jean-Grégoire Ducoin (CPPM), Jean-Luc Atteia (IRAP), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Dalya Akl (NYUAD), Camila Angulo (UNAM), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García-García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Asuka Kuwata (UNAM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), N. A. Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Antonio de Ugarte Postigo (LAM), Ziqi Wang (GXU) and Defeng Kong (GXU) report: We imaged the field of the SVOM GRB 260303A (Wang et al., GCN Circ. 43901) using the DDRAGO two-channel wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2026-03-03 06:02:58 to 06:24:06 UTC (from 81 seconds after the trigger or 30 seconds after the notice until to 24 minutes after the trigger) and obtained 700 seconds of simultaneous exposure in the 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 just outside the ECLAIRs error circle (Wang et al., GCN Circ. 43901) at: RA(J2000) = 06:12:45.06 = 93.1877 degrees Dec(J2000) = +41:09:04.4 = 41.1512 degrees with an uncertainty of 0.5 arcsec. The preliminary magnitudes derived for that source are: r = 18.69 +/- 0.01 z = 18.19 +/- 0.02 The source is observed to rise and then fall in both r and z. Further observations 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/43902. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...