Type III bursts produced by power law injected electrons in Maxwellian background coronal plasmas

Abstract

Simulations are presented for coronal type III bursts produced by injection of energetic electrons with power law speed spectra onto open magnetic field lines embedded in an otherwise unmagnetized Maxwellian background coronal plasma, including quasi‐linear wave‐particle interactions and nonlinear wave‐wave processes. The simulations show that although fast electrons with speeds >0.3c are injected, they are important only to the onset and not to the peak of fp emission, where fp is the local electron plasma frequency. Instead, slower beam electrons are the major drivers of the peak fp emission. Therefore, the type III beam speeds derived from the drift rates of peak fp emission are less than the typical speeds of c/3 observed for coronal type III bursts. This occurs mainly because the number of fast beam electrons with speeds >0.3c is much less than the slower ones, causing weaker fp emission from these fast beam electrons. Comparisons are made with injected electrons having Maxwellian spectra. We find that type III beams are faster when the injection has power law spectra, since there are more fast electrons injected than for Maxwellian spectra. These results suggest that type III beams produced in the corona with Maxwellian background particle distributions and either power law or Maxwellian spectra can account only for the lower half of the observed range 0.1–0.6c of type III beam speeds but not for the upper half.