TITLE: GCN CIRCULAR NUMBER: 43455 SUBJECT: EP260119a: COLIBRÍ photometric redshift z ≈ 5.6 DATE: 26/01/19 18:02:49 GMT FROM: Alan Watson at UNAM <alan@astro.unam.mx> Francis Fortin (IRAP), Leonardo García García (UNAM), Camila Angulo (UNAM), Nikos Mandarakas (LAM), Alan M. Watson (UNAM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (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), 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 EP260119a (Jiang et al., GCN Circ. 43447; Cheng et al., GCN CIrc. 43449) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-01-19 09:00 to 13:37 UTC (from 8.7 to 13.4 hours after the trigger) and obtained 105, 53, 97, and 32 minutes of exposure in the r, i, z, and y 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. Our longer time interval and multi-filter photometry allows us to estimate the decay index and the photometric redshift of the optical counterpart reported by ourselves in Fortin et al. (GCN Circ. 43450) and confirmed by Eyles-Ferris et al. (GCN Circ 43452). In the z band, we see a shallow decay with a temporal index of -0.44 +/- 0.19. The counterpart is detected in all four bands. After correcting for the Galactic foreground extinction corresponding to a reddening of E(B-V) = 0.011 mag (Schlafly & Finkbeiner 2011) and fitting a power-law model to the rizy-bands using a no dust extinction curve, we derive a photometric redshift of z = 5.62 with formal errors of +0.02-0.03 (1-sigma c.l.). We caution that our magnitudes are not strictly simultaneous, but nevertheless the break from z to i to r is much stronger than can be accounted for by this effect. 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/43455. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...