TITLE: GCN CIRCULAR NUMBER: 44102 SUBJECT: GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions DATE: 26/03/24 12:34:17 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo@gmail.com> Antonio de Ugarte Postigo (LAM), Fredd Sánchez Álvarez (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), 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), Benjamin Schneider (LAM) SVOM BA1 and SVOM BA2 report: We imaged the field of the SVOM GRB 260321A (Brunet et al., GCN Circ. 44071) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2026-03-22 06:35:41 to 09:32:17 UTC (from 12.39 to 15.34 hours after the trigger) and obtained 128 minutes of exposure in the r and z filters. A second comparison epoch was observed from 2026-03-24 06:16:18 to 09:07:59 UTC (from 60.07 to 62.93 hours after the trigger) again in r and z with 128 min of exposure. The data were reduced and coadded with the ASU pipeline, and analyzed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. In the comparison and subtraction of the two epochs, we do not detect any credible new source at any of the FXT source positions (Zou et al., GCN Circ. 44086) down to the following 3-sigma limit: r > 24.7 z > 23.6 These upper limits supersede the ones reported by de Ugarte Postigo et al. (GCN Circ. 44078). 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/44102. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...