TITLE: GCN CIRCULAR NUMBER: 41393 SUBJECT: GRB 250814A: Further COLIBRÍ optical upper limit DATE: 25/08/15 14:48:30 GMT FROM: Alan Watson at UNAM <alan@astro.unam.mx> Enrique Moreno Méndez (UNAM), Francesco Magnani (CPPM), Jean-Grégoire Ducoin (CPPM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Fredd Sánchez Álvarez (UNAM), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (OCA), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), and Antonio de Ugarte Postigo (LAM) report: We imaged the field of the Fermi and Swift GRB 250814A (Fermi team, GCN Circ. 41357, Caputo et al. GCN Circ. 41358) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-08-15 03:20 to 04:48 UTC (from 19.8 to 21.2 hours after the trigger) and obtained 64 minutes of exposure in the r filter. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). 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 the stacked image, we do not detect any new source at the XRT source position (Caputo et al. GCN Circ. 41358) or possible optical and infrared counterpart position (Karambelkar et al. GCN Circ. 41377; Castro-Tirado et al., GCN Circ. 41381; Ahumada et al. GCN Circ. 41382; D'Avanzo et al. GCB Circ. 41391; Kumar et al. GCN Circ. 41392) down to the following 3-sigma limit: r > 23.6 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/41393. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...