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

$\textit{Context.}$ 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. $\textit{Aims.}$ 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. $\textit{Methods.}$ 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. $\textit{Results.}$ 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 ($\sim4\times10^{5}$ Jy). Equivalently, circularly polarized radio bursts can be detected up to a distance of 20 pc (encompassing the known exoplanets 55 Cnc, Tau Bo\"{o}tis, and Upsilon Andromedae) assuming the level of emission is $10^{5}$ times stronger than the peak flux of Jupiter's decametric burst emission ($\sim6\times10^{6}$ Jy).