The search for radio emission from exoplanets using LOFAR beam-formed observations

International audienceThe detection of exoplanetary magnetic fields is one of the most elusive hunts in exoplanet science today. Observing the magnetic field of an exoplanet will give valuable information to constrain their interior structure, atmospheric escape, and the nature of any star-planet interactions. Additionally, the magnetic fields on Earth-like exoplanets might help contribute to their sustained habitability by deflecting energetic stellar wind particles. The most promising method to detect exoplanet magnetic fields is radio emission observations since this method is not susceptible to false positives. All the magnetized planets and moons in our Solar System emit in the radio using the Cyclotron Maser Instability (CMI) mechanism. To date, many ground-based observations conducted to find exoplanet radio emission have resulted in non-detections. In this talk, we discuss our ongoing observational campaign searching for exoplanetary radio emissions using beam-formed observations with the Low Band of the Low-Frequency Array (LOFAR). To date we have observed three exoplanetary systems: 55 Cnc, Upsilon Andromedae, and Tau Boötis. These planets were selected according to theoretical predictions, which indicated them as among the best candidates for an observation. Data analysis is currently ongoing. In order to test, validate, and quantify the sensitivity reached with our LOFAR pipeline, we apply it to a LOFAR observation of Jupiter's magnetospheric radio emission in which the signal from Jupiter is attenuated. The idea is simple: we observe Jupiter, divide its signal by a fixed factor before adding it to an observation of sky background, thereby creating an artificial dataset best described as "Jupiter as an exoplanet". We then run our pipeline and check whether the (attenuated) radio signal from Jupiter is detected. The maximum factor by which we can divide Jupiter's signal and still achieve a detection gives the sensitivity of our setup. We find that circularly polarized exoplanetary radio bursts can be detected up to a distance of 20 pc assuming the level of emission is 105 times stronger than the peak flux of Jupiter's decametric burst emission