GMRT radio observations of the transiting extrasolar planet HD 189733b at 244 and 614 MHz

We report a sensitive search for meter-wavelength emission at 244 and 614 MHz from HD 189733 b, the nearest known extrasolar transiting planet of "hot-Jupiter" type. To discriminate any planetary emission from possible stellar or background contributions, we observed the system for 7.7 h encompassing the planet's eclipse behind the host star. These GMRT observations provide very low (3α) upper limits of 2 mJy at 244 MHz and 160 μJy at 614 MHz. These limits are, respectively, about 40 and 500 times deeper than those reported recently at a nearby frequency of 340 MHz. Possible explanations of our non-detection include: (1) the Earth being outside the planet's emission beam; (2) its highly variable emission with more rapid flaring than the temporal sampling in our observations; (3) the planetary emission being intrinsically too weak; or more likely; (4) the emission being predominantly at lower frequencies because of a weak planetary magnetic field. We briefly discuss these possibilities and the constraints on this exo-planetary system environment.