In search of radio emission from exoplanets: GMRT observations of the binary system HD 41004

This paper reports Giant Metrewave Radio Telescope (GMRT) observations of the binary HD 41004 that are among the deepest images ever obtained at 150 MHz and 400 MHz in the search for radio emission from exoplanets. The HD 41004 system consists of a K1 primary and an M2 secondary; both stars are host to massive planets / brown dwarfs. Analogous to planets in our solar system that emit at radio wavelengths due to their strong magnetic fields, one or both of the planets in the HD 41004 binary might emit at radio wavelengths and various models predict that HD 41004Bb might have one of the largest expected flux densities at 150 MHz. Our observations at 150 MHz cover the entire orbital period of HD 41004Bb. We do not detect radio emission, setting limits of 1.8 mJy (3σ) at 150 MHz and 0.12 mJy (3σ) at 400 MHz. Both limits are factors of a few to more than an order of magnitude below various predictions. We attribute the lack of detection either to a low conversion efficiency of input power to planetary magnetospheres (<~ 10%) or strong beaming, with the Earth lying outside of the beaming cone.