Polarization of Multiple-Frequency Band Solar Spike Bursts

A model for the generation mechanism for multiple frequency bands in solar spike bursts is extended to predict the degree of circular polarization of the spike burst radiation in the source region. In this model, several adjacent electrostatic Bernstein modes are excited by the electron-cyclotron maser instability and subsequent nonlinear coalescence of Bernstein waves produces transverse magnetoionic waves which freely propagate out of the source region at the foot of a coronal loop to an observer. The emission rates for the coalescence processes between two Bernstein waves to produce transverse x-mode and o-mode waves are compared in order to predict the polarization state of the product radiation. Low degrees of circular polarization favouring the x-mode are predicted to occur over a wide range of parameter space. The range of emission angles is shown to vary between each frequency band, which further constrains the number of simultaneously observable anharmonic bands than predicted in the earlier model. The consistency of these predictions with currently available polarization observations is discussed.