TITLE: GCN CIRCULAR NUMBER: 43329 SUBJECT: GRB 260101A: COLIBRÍ optical upper limits DATE: 26/01/05 06:51:12 GMT FROM: Jean-Luc Atteia at IRAP <jean-luc.atteia@irap.omp.eu> Jean-Luc Atteia (IRAP), Noémie Globus (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Dalya Akl (NYUAD), Camila Angulo (UNAM), 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), Nikos Mandarakas (LAM), Kin Ocelotl López (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 GRB 260101A (Fermi GBM team, GCN Circ. 43284; Cenko et al., GCN Circ. 43285; Pérez-Fournon et al., GCN Circ. 43286; de Ugarte Postigo et al., GCN Circ. 43287; Beardmore et al., GCN Circ. 43289; Lipunov et al., GCN Circ. 43290; D'Avanzo et al., GCN Circ. 43291; SVOM/GRM team et al., GCN Circ. 43292; Saccardi et al., GCN Circ. 43293; Wang et al., GCN Circ. 43294; Hristov et al., GCN Circ. 43297; Globus et al., GCN Circ. 43312; Klinger et al., GCN Circ. 43318) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2026-01-05 03:38 to 05:46 UTC (98.7 hours to 100.8 hours after the trigger) and obtained 94 minutes of simultaneous exposure in the 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 our stacked images, the previously detected afterglow (Cenko et al., GCN Circ. 43285; Pérez-Fournon et al., GCN Circ. 43286; Globus et al., GCN Circ. 43312; Klinger et al., GCN Circ. 43318) has faded beyond our 5-sigma detection limit: r > 22.96, z > 22.42. 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/43329. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...