TITLE: GCN CIRCULAR NUMBER: 43267 SUBJECT: GRB 251230A: GOTO optical upper limit DATE: 25/12/30 11:26:15 GMT FROM: Rhaana Starling at U of Leicester <rlcs1@leicester.ac.uk> R. Starling, A. Kumar, G. Ramsay, D. O’Neill, B. P. Gompertz, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, S. Belkin, B. Godson, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares report on behalf of the GOTO collaboration: We report on observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) that serendipitously covered the field of GRB 251230A detected by Swift (Lanava et al., GCN 43252; Osborne et al., GCN 43263) and likely coincident with an Einstein Probe trigger (Wang et al., GCN 43259). Two sets of observations were performed by GOTO-North at 2025-12-30 06:01:45 UT and 2025-12-30 06:16:08 UT. Each observation consisted of 4x45 s exposures in the GOTO L-band (400-700 nm). Images were processed using the GOTO pipeline. We do not detect the optical counterpart (Lanava et al., GCN 43252; Li et al., GCN 43255; Busmann et al., GCN 43258; Masi et al., GCN 43260; Ghosh et al., GCN 43262; Ma et al., GCN 43265) down to 3-sigma limiting magnitudes of L >20.8 (AB) and L >20.6 (AB) at 4.7 hours and 4.9 hours post-trigger, respectively. Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are 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). View this GCN Circular online at https://gcn.nasa.gov/circulars/43267. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...