TITLE: GCN CIRCULAR NUMBER: 43077 SUBJECT: EP251212a : COLIBRÍ optical upper limit DATE: 25/12/12 14:49:35 GMT FROM: J.-G. Ducoin at CPPM <ducoin@cppm.in2p3.fr> Jean-Grégoire Ducoin (CPPM), Enrique Moreno Méndez (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (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), Nikos Mandarakas (LAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM): We imaged the field of the EP251212a (Yang et al., GCN Circ. 43076) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-12-12T11:08:54.118 to 11:27:56.049 UTC (from 4.94 to 5.25 hours after the trigger) and obtained 960 seconds of simultaneous exposure in the r and z filters. The data were reduced, coadded and analyzed with the COLIBRÍ pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and was not corrected for Galactic extinction. In the stacked image, we do not detect any new source at the WXT uncertainty region (Yang et al., GCN Circ. 43076) down to the following 5-sigma limit: r > 22.59 z > 21.41 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/43077. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...