Optically Thick Gyrosynchrotron Emission from Anisotropic Electron Distributions

We present a numerical study of optically thick gyrosynchrotron emission produced by fast electrons with anisotropic pitch-angle distributions. The anisotropy is found to affect substantially both radiation spectra and polarization. The harmonic nature of gyrosynchrotron emission becomes more pronounced for the anisotropic case. The effect is entirely provided by a reduction of the self-absorption coefficient due to pitch-angle anisotropy; thus, it is essentially different from electron cyclotron maser emission, which is due to wave amplification under negative absorption. The paper studies the dependences of the emission on the involved parameters and discusses possible applications of the results to observations of microwave solar radio bursts.