GCN Circular 45995
Subject
GRB 261017A: COLIBRÍ optical upper limit
Event
Date
2026-10-20T14:05:40Z (11 hours ago)
From
Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo@gmail.com>
Via
email
Antonio de Ugarte Postigo (LAM), William H. Lee (UNAM), Stéphane Basa (UAR Pytheas), 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), 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), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), Alan M. Watson (UNAM) report:
We imaged the field of GRB 261017A, detected by Fermi (Fermi GBM team, GCN Circ. 45973), Swift (Siegel
et al. GCN Circ. 45974) and KONUS-Wind (Ridnaia et al. GCN Circ. 45990) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-10-20 10:44:10 to 12:36:17 UTC (from 66.6514 to 68.5367 hours after the trigger) and obtained 69 minutes of exposure in the r filter.
The data were reduced and coadded with the COLIBRÍ pipeline and analysed with the CPPM and ASU pipelines. 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 at the XRT source position (Beardmore et al., GCN Circ. 45977) down to the following 3-sigma limit:
r > 24.2 mag
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.