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GMRT radio observations of the transiting extrasolar planet HD189733b at 244 and 614 MHz

We report a sensitive search for meter-wavelength emission at 244 and 614 MHz from HD189733b, 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 hours encompassing the planet's eclipse behind the host star. These GMRT observations provide very low (3 sigma) upper limits of 2 mJy at 244 MHz and 160 micro-Jy 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.