TITLE: GCN CIRCULAR NUMBER: 41685 SUBJECT: GRB 250903A: LCO optical afterglow detection DATE: 25/09/03 21:28:52 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es> I. Pérez-Fournon, F. Poidevin (IAC and ULL), D. Cano-Morales, A.E. Hernández-Díaz, I. Correa-Plasencia (ULL), and A. López-Oramas (IAC and ULL) We observed the field of GRB 250903A detected by SVOM/ECLAIRs (Maiolino et al., GCN 41677) and SVOM/MXT (Götz et al., GCN 41681) with one of the two 1-m telescopes of the Las Cumbres Observatory Global Telescope network (LCO) equipped with Sinistro cameras located at the LCO node at Siding Spring Observatory, Australia. The observation, of 300 seconds in the SDSS-r filter, started at 2025-09-03 19:12:07 UT, about 1.78 hr after the SVOM/ECLAIRs trigger. We clearly detect an uncatalogued source within the SVOM/ECLAIRs (Maiolino et al., GCN 41677) and SVOM/MXT (Götz et al., GCN 41681) error circles at a position consistent with the one reported by An et al. (TRT R band, GCN 41679) and Xin et al. (SVOM/VT VT_B and VT_R, GCN 41684). We measure a magnitude of r = 20.29 +/- 0.10, calibrated with the Legacy Surveys DR10 catalog and not corrected for Galactic extinction. This work makes use of observations from the Las Cumbres Observatory global telescope network program IAC2025B-008 (SGLF). View this GCN Circular online at https://gcn.nasa.gov/circulars/41685. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...