TITLE: GCN CIRCULAR NUMBER: 42638 SUBJECT: GRB 251111A: SVOM/COLIBRÍ (FM-GFT) optical counterpart detection DATE: 25/11/11 06:23:52 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo@gmail.com> Diego López-Cámara (UNAM), Antonio de Ugarte Postigo (LAM), Alan M. Watson (UNAM), Benjamin Schneider (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), 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), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), N. A. Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Yehao Cheng (SWIFAR,YNU), Boting Wang (YNAO): We imaged the field of the SVOM GRB 251111A (Cheng et al., GCN Circ. 42637) using the DDRAGO two-channel wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-11-11 05:21:36 to 05:37:03 UTC (from 11.4 to 26.8 minutes after the trigger) and obtained 13 minutes of simultaneous exposure in the r and z filters. 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 detect an uncatalogued source revealed by image subtraction using PanSTARRS as template and consistent with the ECLAIRs 7.55 arcmin error circle (Cheng et al., GCN Circ. 42637) at: RA(J2000) = 02:09:26.82 = 32.361770 degrees Dec(J2000) = 05:13:40.4 = 5.227888 degrees with an uncertainty of 0.5 arcsec. The preliminary magnitude derived for that source is: r = 21.35 +/- 0.05 z = 20.27 +/- 0.05 The source fades during our observations, confirming that it is the optical afterglow of the GRB. The red r-z color might indicate a moderately high redshift or extinction due to dust. 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/42638. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...