Multi-site follow-up observations of the first possible exoplanet radio detection

Many of the discovered exoplanets are unlike our Solar System planets. Characterizing these alien worlds offers insights into planet formation, planetary system architectures, and even the possibility of planetary habitability. Astronomers have developed a variety of techniques to probe their radii, masses, temperatures, orbital parameters, and atmospheric compositions. However, one of the most important planetary properties is not yet directly detected despite decades of searching: the presence of a magnetic field.

Observing planetary auroral radio emission is the most promising method to detect exoplanetary magnetic fields. All of the gas giants planets in our Solar System have a magnetic field, and theoretical studies predict that many exoplanets should as well. Observations of exoplanet magnetic fields would yield constraints on planetary properties difficult to study, such as interior structure, atmospheric escape, and star-planet interactions. Magnetic drag could be an important factor in the dynamics of exoplanetary atmospheres. Additionally, magnetic fields may contribute to the sustained habitability of terrestrial exoplanets.

Recently, we published the first possible detection of an exoplanet in the radio (Turner et al. 2021). We observed the exoplanetary system tau Boo using LOFAR beamformed observations. We tentatively detected slowly variable and bursty emission from 14-30 MHz. Assuming the emission is from the planet, we derived a maximum surface polar magnetic field for tau Boo b between ~5-11 G. The magnetic field and emission strengths we derived are consistent with theoretical predictions, and if this detection is confirmed it will place important constraints on dynamo theory.

In this talk, we present the first results of an extensive multi-site follow-up campaign to confirm the radio detection of tau Boo b. Our campaign consists of low-frequency radio data from 15-62 MHz taken simultaneously from LWA-SV, NenuFAR, LOFAR, and UTR-2. Additionally, we monitored the stellar light curves for stellar flares simultaneously with Evryscope and partially with TESS. The observations cover most of the orbit multiple times to search for periodicity of the detected signal.