TITLE: GCN CIRCULAR NUMBER: 43874 SUBJECT: EP260227a: COLIBRÍ optical observations DATE: 26/02/28 09:50:46 GMT FROM: nikos.mandarakas@lam.fr Nikos Mandarakas (LAM), Camila Angulo (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Asuka Kuwata (UNAM), Diego López-Cámara (UNAM), 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 EP260227a (Wang et al., GCN Circ. 43869) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-02-28 07:51:00 to 08:49:14 UTC (from 11.64 to 12.61 hours after the trigger) and obtained 44 minutes of simultaneous exposure in the r and z filters. The data were reduced, coadded, calibrated, and analysed with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. We detected the optical counterpart reported by Eyles-Ferris et al. (GCN 43867), Li et al. (GCN 43868), Fu et al. (GCN 43873), at a preliminary magnitude of: r = 21.4644 +/- 0.0680 z = 20.8905 +/- 0.0745 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/43874. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...