AT2023fhn (the Finch): a Luminous Fast Blue Optical Transient at a large off set from its host galaxy

Luminous Fast Blue Optical Transients (LFBOTs) - the prototypical example being AT 2018cow - are a rare class of events whose origins are poorly understood. They are characterised by rapid evolution, featureless blue spectra at early times, and luminous X-ray and radio emission. LFBOTs thus far have been found exclusively at small projected offsets from star-forming host galaxies. We present Hubble Space Telescope, Gemini, Chandra and Very Large Array observations of a new LFBOT, AT2023fhn. The Hubble Space Telescope data reveal a large offset (greater than 3.5 half-light radii) from the two closest galaxies, both at a redshift of 0.24. The isolated environment of AT 2023fhn is in stark contrast with previous events, is challenging to explain with most LFBOT progenitor models, and calls into question the homogeneity of LFBOTs as a class.