The search for radio emission from exoplanets using LOFAR beam-formed observations: Jupiter as an exoplanet

Context. The magnetized solar system planets are strong radio emitters and theoretical studies suggest that the radio emission from nearby exoplanets in close-in orbits could reach intensity levels 10(3)-10(7) times higher than Jupiter's decametric emission. Detection of exoplanets in the radio domain would open up a brand new field of research, however, currently there are no confirmed detections at radio frequencies. Aims. We investigate the radio emission from Jupiter, scaled such that it mimics emission coming from an exoplanet, with low-frequency beam-formed observations using LOFAR. The goals are to define a set of observables that can be used as a guideline in the search for exoplanetary radio emission and to measure effectively the sensitivity limit for LOFAR beam-formed observations. Methods. We observe "Jupiter as an exoplanet" by dividing a LOFAR observation of Jupiter by a down-scaling factor and adding this observation to beam-formed data of the "sky background". Then we run this artificial dataset through our total intensity (Stokes-I) and circular polarization (Stokes-V) processing and post-processing pipelines and determine up to which down-scaling factor Jupiter is still detected in the dataset. Results. We find that exoplanetary radio bursts can be detected at 5 pc if the circularly polarized flux is 10(5) times stronger than the typical level of Jupiter's radio bursts during active emission events (similar to 4 x 10(5) Jy). Equivalently, circularly polarized radio bursts can be detected up to a distance of 20 pc (encompassing the known exoplanets 55 Cnc, Tau Bootis, and Upsilon Andromedae) assuming the level of emission is 10(5) times stronger than the peak flux of Jupiter's decametric burst emission (similar to 6 x 10(6) Jy).