Looking for a Pulse: A Search for Rotationally Modulated Radio Emission from the Hot Jupiter, τ Boötis b

G. Hallinan, S.K. Sirothia, A. Antonova, C.H. Ishwara-Chandra, S. Bourke, J.G. Doyle, J. Hartman and A. Golden

Fig. 2. Light curves for the left circularly polarized flux at the position of τ Boötis b over the course of the observing campaign. Time series at time resolution of 4 seconds and 17 minutes are shown in red and blue respectively, with RMS noise of 65 mJy for the 4 second resolution time series and 4 mJy for the 17 minute resolution time series. No evidence for heightened emission is present during any of the observed orbital/rotational phase of the planet.


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 τ Boötis 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 3σ 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 τ Boötis 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.

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Last Revised: 2012 October 31st