TITLE: GCN CIRCULAR NUMBER: 40907 SUBJECT: GRB 250702F: COLIBRÍ Observations of the Afterglow DATE: 25/07/03 05:31:22 GMT FROM: Margarita Pereyra Talamantes at IA-UNAM Ensenada <mpereyra@astro.unam.mx> Camila Angulo (UNAM), Margarita Pereyra (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Fredd Alvarez (UNAM), Dalya Akl (AUS), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), N. A. Rakotondrainibe (LAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM): We imaged the field of the Swift GRB 250702F (Klingler et al., GCN Circ. 40894) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-07-03 03:53 to 04:03 UTC (from 6.78 to 6.95 hours after the trigger) and obtained 180 seconds of exposure in each of the g, r, and i filters. 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. We detected the optical counterpart reported by Klingler et al. (GCN Circ. 40894), Jelinek et al. (GCN Circ. 40895), Kumar et al. (GCN Circ. 40896), Lipunov et al (GCN Circ. 40899), Martin-Carrillo et al. (GCN Circ. 40900), and de Ugarte Postigo et al (GCN Circ. 40901) at a preliminary magnitude of: g = 19.60 +/- 0.03 r = 19.52 +/- 0.03 i = 19.24 +/- 0.03 Further observations are ongoing. 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/40907. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...