TITLE: GCN CIRCULAR NUMBER: 44595 SUBJECT: EP260512a: COLIBRÍ optical upper limits DATE: 26/05/13 06:18:56 GMT FROM: J.-G. Ducoin at CPPM <ducoin@cppm.in2p3.fr> Diego López-Cámara (UNAM), Jean-Grégoire Ducoin (CPPM), Camila Angulo (UNAM), Rosa L. Becerra (UNAM), Jean-Luc Atteia (IRAP), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of the EP260312a (Liang et al., GCN Circ. 44594), using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-13 04:09 to 04:25 UTC (from 19.6 to 19.9 hours after the trigger and 6 minutes after the release of the GCN) and obtained 14 minutes of simultaneous exposure in the r and z filters. The data were reduced and coadded with the COLIBRÍ ASU 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. In the stacked images and after performing image subtraction using templates from the DESI Legacy Survey (Dey et al. 2019), we do not detect any new source within the WXT error region we do not detect any new source at the WXT error position (Liang et al., GCN Circ. 44594) down to the following 5-sigma limits: r > 23.1 z > 21.9 We note the presence of the quasar 2MASS J14554420+282524 within the WXT region and, considering our upper limits and the low SNR reported by the Einstein Probe Team (Liang et al., GCN Circ. 44594), we cannot rule out the possibility that the trigger is related to this source. We thank the staff of the Observatorio Astronómico Nacional at Sierra de San Pedro Mártir, as well as the technical and engineering teams at CEA, CPPM, IRAP, LAM, OHP, OSU Pytheas, and UNAM. 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/44595. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...