TITLE: GCN CIRCULAR NUMBER: 44719 SUBJECT: EP260527a: COLIBRÍ optical detection DATE: 26/05/28 06:36:51 GMT FROM: Francesco Magnani at Aix-Marseille Université, CPPM/CNRS <francesco.magnani.work@gmail.com> Edilberto Aguilar-Ruiz (UNAM), Francesco Magnani (CPPM), Alan M. Watson (UNAM), Rosa L. Becerra (UNAM), Antonio de Ugarte Postigo (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (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), Diego López-Cámara (UNAM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), and Benjamin Schneider (LAM) and report: We imaged the field of the EP260527a (J. Yang et al, GCN Circ. 44718) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-28 04:13 to 06:05 UTC (from 21.90 to 23.76 hours after the trigger) and obtained 18, 62, and 82 minutes of exposure in the g, r, and z filters. The data were reduced and coadded 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 (in this case with a relatively high value of A_v = 1.1 mag, according to Schlafly et al. 2011). In the stacked images, we detect an uncatalogued source within the FXT uncertainty region at: RA (J2000) = 12:52:13.13 = 193.05473 degrees Dec (J2000) = +01:28:56.8 = 1.48244 degrees The preliminary magnitudes derived for that source is: g = 22.25 +/- 0.32, r = 22.19 +/- 0.17, z = 21.52 +/- 0.15. The detection in g suggests that it is not a high-redshift event. Further observations are ongoing. 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/44719. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...