TITLE: GCN CIRCULAR NUMBER: 41121 SUBJECT: GRB 250717B: COLIBRÍ optical upper limit DATE: 25/07/18 21:30:53 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra@roma2.infn.it> Enrique Moreno Méndez (UNAM), Francis Fortin (IRAP), Rosa L. Becerra (U Roma), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Fredd Alvarez (UNAM), Camila Angulo (UNAM), Dalya Akl (AUS), Sarah Antier (OCA), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM): We imaged the field of the Fermi/GBM GRB 250717B (Fermi GBM Team et al., GCN Circ. 41107) at the Swift/BAT-GUANO localization (Ronchini et al., GCN Circ. 41110) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-07-18 09:16 to 11:31 UTC (from 19.5 to 21.8 hours after the trigger) and obtained 101 minutes of exposure in the i 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, 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 Swift/BAT-GUANO error region (Ronchini et al., GCN Circ. 41110), including the XRT candidate position (Dichiara et al., GCN Circ. 41119) down to the following 5-sigma limit: i > 21.8 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/41121. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...