A Volume-Limited Radio Search for Magnetic Activity in 140 Exoplanets with the Very Large Array

TL;DR

This study conducted the largest and most sensitive radio survey to date of 140 exoplanets within 17.5 parsecs, finding one potential star-planet interaction signal and setting upper limits on radio emissions for most targets.

Contribution

It provides the first large-volume, sensitive GHz radio survey of exoplanetary systems, expanding the sample size and sensitivity compared to previous targeted searches.

Findings

Detected one candidate signal with high circular polarization.

Set upper limits on radio luminosity for 139 exoplanet systems.

Results are consistent with previous non-detections and theoretical predictions.

Abstract

We present results from a search for radio emission in 77 stellar systems hosting 140 exoplanets, predominantly within 17.5 pc using the Very Large Array (VLA) at $4-8$ GHz. This is the largest and most sensitive search to date for radio emission in exoplanetary systems in the GHz frequency range. We obtained new observations of 58 systems, and analyzed archival observations of an additional 19 systems. Our choice of frequency and volume limit are motivated by radio detections of ultracool dwarfs (UCDs), including T dwarfs with masses at the exoplanet threshold of $\sim\!13\,M_J$. Our surveyed exoplanets span a mass range of $\approx\,10^{-3}-10\,M_J$ and semi-major axes of $\approx\,10^{-2}-10\,$AU. We detect a single target - GJ 3323 (M4) hosting two exoplanets with minimum masses of 2 and 2.3$\,M_\oplus$ - with a circular polarization fraction of $\approx\,40\%$; the radio luminosity agrees with its known X-ray luminosity and the G\"udel-Benz relation for stellar activity suggesting a likely stellar origin, but the high circular polarization fraction may also be indicative of star-planet interaction. For the remaining sources our $3\sigma$ upper limits are generally $L_\nu\lesssim\,10^{12.5}\,\mathrm{erg}\,\mathrm{s}^{-1}\,\mathrm{Hz}^{-1}$, comparable to the lowest radio luminosities in UCDs. Our results are consistent with previous targeted searches of individual systems at GHz frequencies while greatly expanding the sample size. Our sensitivity is comparable to predicted fluxes for some systems considered candidates for detectable star-planet interaction. Observations with future instruments such as the Square Kilometer Array and Next Generation Very Large Array will be necessary to further constrain emission mechanisms from exoplanet systems at GHz frequencies.