TITLE: GCN CIRCULAR NUMBER: 38445 SUBJECT: GRB 241204A: COLIBRÍ Optical Upper Limit DATE: 24/12/05 21:16:51 GMT FROM: Dornic Damien <dornicdamien@gmail.com> Francesco Magnani (CPPM), J.-G. Ducoin (CPPM), Damien Dornic (CPPM), Alan M. Watson (UNAM), Margarita Pereyra (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), S. Antier (OCA), Jean-Luc Atteia (IRAP), Nathaniel R. Butler (ASU), Francis Fortin (IRAP), Simona Lombardo (LAM), and report: We imaged the field of GRB 241204A detected by Fermi/LAT (Bissaldi et al., GCN 38436) and Fermi/GBM (Godwin et al., GCN 38441) during the commissioning of the COLIBRÍ (SVOM/F-GFT) telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico. The observations started 23.9 hours after the GRB trigger. We obtained 1200 seconds of exposure with the engineering test camera in a red filter that approximates SDSS r. The observation covers 13 arcmin field of view centered to the LAT coordinates. The data were reduced using custom software and then analysed and calibrated against the PS1 catalog using the STDWeb service (Karpov et al. 2022). We estimate an upper limit of 20.6 mag (10 sigma). This limiting magnitude is consistent with other optical observations of MASTER (Lipunov et al., GCN Circ. 38440) and DDOTI (Becerra et al., GCN Circ. 38442). We warmly thank the COLIBRI engineering team and the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/38445. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...