TITLE: GCN CIRCULAR NUMBER: 41069 SUBJECT: EP candidate (ID=08500000365): COLIBRÍ optical Upper limit DATE: 25/07/12 05:52:18 GMT FROM: Kin Océlotl Cuauhtli López Mendoza at Instituto de Astronoma, UNAM <koclopez@astro.unam.mx> Kin Ocelotl López (UNAM), Rosa L. Becerra (U Roma), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (AUS), Sarah Antier (OCA), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM): We imaged the field of the EP alert (ID=08500000365 and trigger time T= 2025-07-11 17:10:56.00) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-07-12 03:40 to 03:59 UTC (from 10.5 to 10.8 hours after the trigger and starting 1.3 hours after the arrival of the notice) and obtained 16 minutes of exposure in the i filter. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction (which is considerably high due to the proximity to the Galactic plane). In our stacked image, and after performing image subtraction using Pan-STARRS as a reference, we do not detect any new source at the WXT position, down to the following 5-sigma limit: i > 21.3 Nevertheless, we noticed the presence inside the WXT error box of the eclipsing binary (Gaia DR3 4292676364775382144) and an RR Lyrae star (Gaia DR3 4292676394808888448), suggesting that the alert is likely associated with one of these objects. 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/41069. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...