Looking for a Pulse: A search for Rotationally Modulated Radio Emission from the Hot Jupiter, Tau Bootis b

TL;DR

This study conducted deep 150 MHz radio observations of Tau Bootis b to detect rotationally modulated emission, setting the most stringent upper limits and exploring planetary magnetic field and beaming hypotheses.

Contribution

First deep 150 MHz radio observation of Tau Bootis b with extensive orbital coverage, establishing the tightest upper limits on its radio emission.

Findings

No detection of radio emission, with an upper limit of 1.2 mJy.

Results suggest Tau Bootis b's magnetic field may be too weak or emission beaming misses Earth.

Sets new constraints on hot Jupiter radio emission models.

Abstract

Hot Jupiters have been proposed as a likely population of low frequency radio sources due to electron cyclotron maser emission of similar nature to that detected from the auroral regions of magnetized solar system planets. Such emission will likely be confined to specific ranges of orbital/rotational phase due to a narrowly beamed radiation pattern. We report on GMRT 150 MHz radio observations of the hot Jupiter Tau Bootis b, consisting of 40 hours carefully scheduled to maximize coverage of the planet's 79.5 hour orbital/rotational period in an effort to detect such rotationally modulated emission. The resulting image is the deepest yet published at these frequencies and leads to a 3-sigma upper limit on the flux density from the planet of 1.2 mJy, two orders of magnitude lower than predictions derived from scaling laws based on solar system planetary radio emission. This represents the most stringent upper limits for both quiescent and rotationally modulated radio emission from a hot Jupiter yet achieved and suggests that either a) the magnetic dipole moment of Tau Bootis b is insufficient to generate the surface field strengths of > 50 Gauss required for detection at 150 MHz or b) Earth lies outside the beaming pattern of the radio emission from the planet.