GRB 241108A: Further COLIBRÍ Upper Limits on the Optical Counterpart

We again imaged the field of GRB 241108A detected by SVOM/ECLAIRs (Sadibekova et al., GCN Circ. 38132) during the commissioning of the COLIBRÍ (SVOM/F-GFT) telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico. We observed with the engineering test camera in a red filter that approximates SDSS r. The data were reduced using custom software and then analysed and calibrated against the PS1 catalog using the STDWeb service. Our field is centered on the XRT source detected at 08:14:33.07 -07:05:09.9 J2000 (Burrows et al., GCN Circ. 38139). In 7080 seconds of exposure from 2024-11-09 09:01 to 12:52 UTC (1.08 to 1.24 days after the trigger), we detect no new sources within the XRT uncertainty region to a 3-sigma limiting AB magnitude of: r > 23.6 We do detect a two point source within the uncertainty region and one just outside it, but these are also present in the earlier PS1 image at a similar magnitude and therefore are unlikely to be the optical counterpart of the GRB. We warmly thank the COLIBRÍ engineering team and the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir. We warmly thank the GRANDMA IJCLAB team and S. Karpov for the access of the STDWeb service for STDPipe.