TITLE: GCN CIRCULAR NUMBER: 43153 SUBJECT: IceCube-251218A: COLIBRÍ optical upper limits DATE: 25/12/19 08:35:20 GMT FROM: antier@ijclab.in2p3.fr Sarah Antier (IJCLAB), Enrique Moreno Méndez (UNAM), Noémie Globus (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (AUS), 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), Nikos Mandarakas (LAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), N. A. Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), and Antonio de Ugarte Postigo (LAM) report: We observed the field of the IceCube-251218A (GCN 43151) (bronzetrack) event with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir. We observed four pointings centred on (RA, Dec) = (353.8851, 44.3568), (353.3414, 44.3590), (353.8784, 43.9697), and (353.3374, 43.9697) between 2025-12-19 02:26 UTC and 03:10 UTC (from 6.09 to 6.59 hours after the trigger). At each pointing we obtained 8 minutes of simultaneous exposure in r and z over a field of 26 x 26 arcmin. These pointings cover a region of approximately 1 x 1 degree centered on (RA, Dec) = (353.60, 44.15) and cover most of the 90% uncertainty region. The data were coadded with the COLIBRÍ ASU pipeline and analysed in STDWeb/STDPipe (Karpov 2025). Comparing our observations (and after performing image subtraction) against Pan-STARRS DR1, we detect no evident uncatalogued sources within the observed fields to a 10-sigma limiting AB magnitudes of: r > 21.9 and z > 20.8 These values are not corrected for the Galactic extinction. We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/43153. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...