TITLE: GCN CIRCULAR NUMBER: 42367 SUBJECT: IceCube-251018A: DDOTI Optical Upper Limit DATE: 25/10/19 07:31:09 GMT FROM: Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra@astro.unam.mx> Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Camila Angulo Valdez (UNAM), Sahil Atri (U Roma), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM), Margarita Pereyra (UNAM) and Eleonora Troja (U Roma) report: We observe the field of the IceCube-251018A (gold) event (IceCube Collaboration, GCN Circ. 42352) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on the Sierra of San Pedro Martir (http://ddoti.astroscu.unam.mx) on the night of 2025-10-19 UTC. DDOTI observed from 03:00 UTC to 06:18 UTC (from T+21.9 h to T+25.2 h after the trigger) with a total exposure of 96 min, covering the total error region reported by IceCube (IceCube Collaboration, GCN Circ 42352). Comparing our observations to the USNO-B1 and PanSTARRS PS1 DR2, we detect no uncatalogued sources within the observed field to a 10-sigma limiting AB magnitude of: w > 20.6. Further observations are planned to assess variability. This value is not corrected for the Galactic extinction. We thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/42367. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...