Type III Bursts in Generalized Lorentzian Plasmas

Type III bursts are produced by subrelativistic electron beams leaving magnetic reconnection regions on the Sun. During its propagation the free energy of a beam is partly converted to Langmuir waves and subsequently to radiation. Generalized Lorentzian (or kappa) distributions are commonly observed for the background plasmas of the solar wind and are inferred for the corona. We report here that treating the background electrons and ions with realistic generalized Lorentzian distributions leads to major qualitative differences in type III bursts from the traditionally assumed Maxwellian distributions. Specifically, the type III beams are much faster and persist much further than for Maxwellian background plasma. Langmuir waves are thus generated at much larger phase speeds and are strongly damped at low phase speeds. Subsequent emission of radiation at the local electron plasma frequency f_p is favored more because the wave number matching conditions involved in the radiation process are easily satisfied. These new results may resolve longstanding issues regarding the speed and persistence of type III beams, and the production of remotely observable levels of f_p emission despite severe losses due to scattering.