{
  "body": "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:\n\nWe 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\n06:35:41 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\n 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.\n\nThe 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.\n\nIn 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:\n\nr > 24.7\nz > 23.6\n\nThese upper limits supersede the ones reported by de Ugarte Postigo et al. (GCN Circ. 44078).\n\nWe 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.\n\nCOLIBRÍ 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.\n\n",
  "bibcode": "2026GCN.44102....1D",
  "subject": "GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions",
  "circularId": 44102,
  "createdOn": 1774355657524,
  "submittedHow": "email",
  "eventId": "GRB 260321A",
  "submitter": "Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo@gmail.com>"
}