TITLE:   GCN CIRCULAR
NUMBER:  45342
SUBJECT: GRB 260809A: SVOM/COLIBRÍ (FM-GFT) optical observation
DATE:    26/08/10 11:01:44 GMT
FROM:    Stephane Basa at UAR Pytheas/OHP, LAM <stephane.basa@lam.fr>

Stéphane Basa (UAR Pytheas), Noémie Globus (UNAM), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), 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), 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), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM),  Alan M. Watson (UNAM) and Frédéric Piron (LUPM) report:

We imaged the field of the SVOM GRB 260809A (Brunet et al., GCN 45331) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2026-08-1 06:18:16
to 09:10:59 UTC (from 15.3 to 18.2 hours after the trigger) and obtained 80x60 seconds of exposure in the z band.

The data were reduced, coadded and analyzed with the ASU and CPPM COLIBRÍ pipelines. The photometry was calibrated using nearby stars from the PanSTARRS DR1r catalog, is in the AB system, and is not corrected for Galactic extinction.

In the stacked image, we detect the optical counterpart (Li et al., GCN 45336; Adami et al., GCN 45338; Rajabov et al., GCN 45339, Izzo et al., GCN 45340) at a preliminary magnitude of:

z = 23.11 +/- 0.16

Further observations are ongoing.

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.