TITLE: GCN CIRCULAR NUMBER: 40102 SUBJECT: IceCube 250406.951: COLIBRÍ/DDRAGO Optical Upper Limit DATE: 25/04/07 06:43:32 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra@roma2.infn.it> Rosa L. Becerra (U Roma), Ny Avo Rakotondrainibe (LAM), Noémie Globus (UNAM), Jean-Grégoire Ducoin (CPPM), Kin Ocelotl López (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA), Jean-Luc Atteia (IRAP), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report: We observed the field of the IceCube 250406.951 (goldtrack) event with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico on the night of 2025-04-07 UTC. COLIBRÍ tiled the IceCube error region from 03:09 UTC to 04:18 UTC (from T+4.3 h to T+5.5 h after the trigger) with a total exposure of 47 minutes. The data were coadded with the COLIBRÍ pipeline and analysed in STDWeb/STDPipe (Karpov 2025). Comparing our observations (and after performing image subtraction) against Pan-STARRS DR2, we detect no evident uncatalogued sources within the observed field to a 5-sigma limiting AB magnitude of: i > 22.2 This non-detection is consistent with the reported by Becerra et al., GCN 40101. This value is not corrected for the Galactic extinction. We warmly thank the COLIBRÍ and DDRAGO engineering teams and the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/40102. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...