TITLE: GCN CIRCULAR NUMBER: 43010 SUBJECT: GRB 251205A: GOTO optical afterglow detection DATE: 25/12/06 11:03:38 GMT FROM: d.s.oneill@bham.ac.uk
D. O'Neill, G. Ramsay, A. Kumar, B. Gompertz, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, S. Belkin, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien,, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, D. Pollacco, J. Casares Vel'azquez, T. Killestein, B. Godson 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 GRB 251205A.
Serendipitous observations from the all-sky survey covered the position of the counterpart (Malesani et al., GCN 43009; Lanava et al., GCN 43005; Lipunov et al., GCN 43006; de Ugarte Postigo et al., GCN 43008) at 2025-12-06 06:12:01 UT, (+6.5h post trigger). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. The counterpart was detected in the GOTO L-band (400-700nm) mag = 18.16 ± 0.12 (AB). Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and not corrected for Galactic extinction.
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).
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