TITLE:   GCN CIRCULAR
NUMBER:  45620
SUBJECT: GRB 260918A: SVOM/COLIBRÍ (FM-GFT) optical upper limits 
DATE:    26/09/18 05:29:47 GMT
FROM:    enriquemm@astro.unam.mx

Enrique Moreno Méndez (UNAM), Marion Guelfand (CPPM), Noémie Globus (UNAM), Stéphane Basa (UAR Pytheas), 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), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM),  Alan M. Watson (UNAM) and Yun Wang (UCB, PMO) report:

We imaged the field of the SVOM GRB 260918A (Zhao et al., GCN Circ. 45619) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2026-09-18
03:49:13 to 05:05:28 UTC (from 0.03 to 1.32 hours after the trigger) and obtained 76 minutes of exposure in the r and z filters. 

The data were reduced and coadded 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 credible new source at the ECLAIRs source position  (Zhao et al., GCN Circ. 45619)  down to the following 5-sigma limit:

r > 23.46,
z > 22.47.

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.