TITLE: GCN CIRCULAR NUMBER: 42858 SUBJECT: GRB 251126A: NOT optical observations DATE: 25/11/27 11:11:11 GMT FROM: Laura Cotter at University College Dublin <laura.cotter@ucdconnect.ie> L. Cotter (UCD), A. Martin-Carrillo (UCD), S.Y. Fu (HUST), J. An (NAOC), G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), T. Pursimo (NOT) report on behalf of a larger collaboration: We observed the optical afterglow of GRB 251126A (Caputo et al., GCN 42843) with the Nordic Telescope (NOT) equipped with the ALFOSC Camera. We obtained 3x300s r-band images with observations starting on 2025-11-26 at 23:31:36 UTC, under good seeing (~1”). However, unfortunately, observations had to be interrupted due to adverse weather conditions. The optical counterpart reported by Swain et al. (GCN 42844), Lipunov et al. (GCN 42847), Fu et al. (GCN 42848), Reguitti et al. (GCN 42849), Broens et al. (GCN 42850), Angulo et al. (GCN 42855), Torres et al. (GCN 42856) and Gupta et al. (GCN 42857) is well detected in our stacked image with an AB magnitude of r = 20.72 ± 0.05 at a mid epoch of 2025-11-26 23:34:06.554 (4.4 hr after the Swift/BAT trigger). This magnitude was calibrated against nearby objects from the Pan-STARRS catalog and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42858. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...