TITLE: GCN CIRCULAR NUMBER: 44572 SUBJECT: GRB 260511B: GOTO optical counterpart detection DATE: 26/05/12 08:15:30 GMT FROM: Sergey Belkin at Monash University <sergey.belkin@monash.edu> S. Belkin, G. Ramsay, D. O'Neill, B. P. Gompertz, M. Wortley, R. Starling, K. Ackley, M. Dyer, J. Lyman, K. Ulaczyk, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, B. Godson, T. Killestein, A. Kumar, M. Pursiainen, on behalf of GOTO collaboration We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to the Fermi/GBM (Fermi GBM team, GCN 44542) and SVOM/ECLAIRs (Godet et al. GCN 44543) triggers for GRB 260511B. Observations started at 2026-05-11 21:09:05 UT, (+10.13h post trigger) in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations (Lyman et al. 2026). We detect the previously reported optical counterpart of GRB 260511B at a position consistent with the source reported by Wu et al. (GCN 44547), Sasada et al. (GCN 44549), Jiang et al. (GCN 44551), Wu et al. (GCN 44552), Vijaykumar et al. (GCN 44561), de Ugarte Postigo et al. (GCN 44565), Lee et al. (GCN 44567), and Li et al. (GCN 44568). The source is detected in the GOTO L-band (400-700 nm) with L=19.45 ± 0.09 AB mag at a mid-time of 2026-05-11 21:44:06 UT (+10.73 h). GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester, the University of Birmingham and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/44572. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...