DETECTION OF LINEAR-POLARIZATION IN THE MICROWAVE EMISSION OF SOLAR ACTIVE REGIONS

We report the detection for the first time of linear polarization in the microwave emission above a Solar Active Region. The observations were made with the Westerbork Synthesis Radio Telescope, taking advantage of the very small bandwidth of a multichannel spectral line receiver. The intensity of the Stokes parameter U, measured at several points close to the line of zero circular polarization, shows a clear sinusoidal trend as a function of lambda2, in accordance to what is expected from Faraday rotation. From the measured period, reasonable values of integral NB(L)dr were derived. Such observations could present in the future a unique way to measure coronal magnetic fields above Active Regions.