TITLE: GCN CIRCULAR NUMBER: 39074 SUBJECT: GRB 250129A: LCO optical observations DATE: 25/01/29 07:54:21 GMT FROM: luca.izzo@inaf.it L. Izzo (INAF-OACn and DARK/NBI), and D. B. Malesani (DAWN/NBI and Radboud Univ.) report: We observed the field of GRB 250129A (Beardmore et al., GCN #39066) with the Sinistro instrument mounted on the 1-m telescope of the LCO network, located at the Cerro Tololo Observatory, Chile. Observations started on 2025 January 29 at 06:40 UT (1.89 hr after the GRB trigger). We obtained a single image of 240 s exposure in each of the SDSS-r and SDSS-i filters. We detect a bright source consistent with the position of the optical afterglow reported by Swift-UVOT (Beardmore et al., GCN #39066) and by other ground-based facilities (Francile, GCN #39065; Schneider et al., GCN #39071; Belkin et al., GCN #39072; Izzo et al., GCN #39073). We measure preliminary magnitudes of r = 17.27 +/- 0.02 mag and i = 17.04 +/- 0.03 (AB), calibrated against nearby stars from the Pan-STARRS catalog. This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 101004719. We also acknowledge the use of the ECSnoopy package by E. Cappellaro. View this GCN Circular online at https://gcn.nasa.gov/circulars/39074. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...