AT2023fhn (the Finch): a luminous fast blue optical transient at a large offset from its host galaxy
Groot, P. J.; Wiersema, K.; Levan, A. J.; Chrimes, A. A.; Stanway, E. R.; Gaspari, N.; Gompertz, B. P.; Malesani, D. B.; Jonker, P. G.; Coppejans, D. L.; Mummery, A.
Netherlands, United Kingdom, South Africa, Denmark
Abstract
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 characterized 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, AT 2023fhn. The Hubble Space Telescope data reveal a large offset (>3.5 half-light radii) from the two closest galaxies, both at redshift z ~ 0.24. The location of AT 2023fhn is in stark contrast with previous events, and demonstrates that LFBOTs can occur in a range of galactic environments.