TITLE: GCN CIRCULAR NUMBER: 43480 SUBJECT: EP260116a: COLIBRÍ observations of a tentative optical rebrightening DATE: 26/01/20 18:36:58 GMT FROM: Alan Watson at UNAM <alan@astro.unam.mx> Alan M. Watson (UNAM), Noémie Globus (UNAM), Nathaniel R. Butler (ASU), Antonio de Ugarte Postigo (LAM) Jean-Luc Atteia (IRAP), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Asuka Kuwata (UNAM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), and Benjamin Schneider (LAM) report: We observed the field of EP260116a (Wang et al., GCN Circ. 43424) with the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope from 2026-01-20 03:54 to 08:25 UTC (from 99.7 to 104.3 hours after the trigger) and obtained 142 and 198 minutes of exposure in the r and z filters, respectively. Conditions were poor with variable transparency. The data were reduced, coadded, calibrated, and analyzed 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. Compared to our observations on the previous night (Butler et al., GCN Circ 43459), we measure an apparent rebrightening of Delta r = -0.17 +/- 0.11 Delta z = -0.30 +/- 0.21 Individually, these apparent rebrightenings are only at the level of about 1.5 sigma. However, together they point to a possibly more significant result, minimally that the decay seen previously appears to have slowed. Further observations are planned and encouraged. 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/43480. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...