TITLE:   GCN CIRCULAR
NUMBER:  43051
SUBJECT: GRB 251206A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
DATE:    25/12/09 14:48:58 GMT
FROM:    Alan Watson at UNAM <alan@astro.unam.mx>

Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Jean-Luc Atteia (IRAP), Noémie Globus (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (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), Kin Ocelotl López (UNAM), 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 Marius Brunet (IRAP) report:

We imaged the field of the SVOM GRB 251206A (Brunet et al., GCN Circ. 43031) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-12-09 04:39 to 0625 UTC (from 55.8 to 57.2 hours after the trigger) and obtained 80 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.

In the stacked image, we do not detect any new source inside the ECLAIRs uncertainty region (Brunet et al., GCN Circ. 43031) to the following 5-sigma limits:

r > 23.3
z > 22.3

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.