TITLE:   GCN CIRCULAR
NUMBER:  45724
SUBJECT: GRB 260922A: COLIBRÍ Confirmation of the Optical Counterpart
DATE:    26/09/24 14:20:41 GMT
FROM:    Rosa Leticia Becerra Godínez at Instituto de Astronomía,  UNAM <rbecerra@astro.unam.mx>

Rosa L. Becerra (UNAM), Antonio de Ugarte Postigo (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM),  Camila Angulo (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), 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) and Alan M. Watson (UNAM) report:

We continued our observations of the field of the Swift GRB 260922A (Page et al., GCN Circ. 45690) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-09-24 02:29 to 03:51 UTC (from 40.48 to 41.86 hours after the trigger) and obtained 64 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.

At the position of the optical counterpart reported in Angulo et al. (GCN Circ. 45699), we do not detect the source in the r band down to the following 3-sigma limit:

r > 23.8.

In the z band, we marginally detect the source with a preliminary magnitude of:

z = 23.15 +/- 0.34.

The observed fading between our two epochs confirms the transient nature of the source and supports its identification as the optical counterpart of GRB 260922A.

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.