Radio Observations of HD 80606 Near Planetary Periastron II. LOFAR Low Band Antenna Observations

All of the giant planets in the solar system generate radio emission via the electron cyclotron maser instability, most notably giving rise to Jupiter's decametric emissions. HD 80606b is a giant planet and it is highly eccentric, leading to predictions that its radio emission may be enhanced substantially near periastron.This paper reports observations with the Low Frequency Array (LOFAR) of HD 80606b near its periastron in an effort to detect radio emissions generated by an electron cyclotron maser instability in the planet's magnetosphere. The reported observations are at frequencies between 30~MHz and 78~MHz, and they are distinguished from previous radio observations of extrasolar planets generally by two factors: (i) They are at frequencies near 50 MHz, much closer to the frequencies at which Jupiter emits (\nu < 40 MHz) and lower than most previously reported observations of extrasolar planets; and (ii) Sensitivities of approximately a few millijanskys have been achieved, an order of magnitude or more below nearly all previous extrasolar planet observations below 100~MHz. We do not detect any radio emissions from HD 80606b and use these observations to place new constraints on its radio luminosity. We also revisit whether the observations were conducted at a time when it was super-Alfvenic relative to the host star's stellar wind, a necessary condition for generating electron cyclotron maser emission. We find that it is, updating previous estimates.