GCN 44046: GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate

2026-03-18T12:06:23.333Z | rev 0 | event: GRB 260316A
Francis Fortin (IRAP), Diego López-Cámara (UNAM), Jean-Grégoire Ducoin (CPPM), Antonio de Ugarte Postigo (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (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), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Missimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM) and Benjamin Schneider (LAM) report:

We imaged the field of the GRB 260316A / EP260316a (Jiang et al., GCN Circ. 44027, GCN Circ. 44034) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-03-18 07:20:28 to 09:50:38 UTC (from 42.8 to 45.3 hours after the trigger) and obtained 111 minutes of simultaneous exposure in the r and z filters.

The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025) and the COLIBRÍ 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.

We still detect the optical counterpart candidate that we previously reported in Fortin et al., GCN Circ. 44037. Template subtraction from 2026-03-17 to 2026-03-18 shows no significant residuals between the two epochs, and therefore does not allow us to conclude on the potential variability of this source.


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.