TITLE: GCN CIRCULAR NUMBER: 40552 SUBJECT: EP250526a: COLIBRÍ optical upper limits DATE: 25/05/27 08:15:01 GMT FROM: Benjamin Schneider at MIT <bschn@mit.edu> Camila Angulo (UNAM), Benjamin Schneider (LAM), Rosa L. Becerra (U Roma), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), 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), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM) and Antonio de Ugarte Postigo (LAM): We imaged the field of the EP250526a (Li et al., GCN Circ. 40550) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-05-27 03:30 to 5:35 UTC (from 8.0 to 10.1 hours after the trigger and 58 minutes after the notice) and obtained 32 minutes of exposure in g, r and i filters (each one). 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 SkyMapper catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked images, we do not detect any new source at the FXT position (Li et al., GCN Circ. 40550) down to the following 3-sigma limit: g > 23.6 r > 23.4 i > 23.0 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/40552. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...