Fast electron generation in quasiperpendicular shocks and type II solar radiobursts

Abstract

The paper is devoted to the theory of type II solar radio bursts caused by collisionless shock waves propagating in the coronal plasma. The model developed is based on the theory of collisionless shock waves, which predicts that a small fraction of ions is reflected from the shock front. This ion beam is unstable and can drive low-frequency waves which, as shown in this paper, are quickly absorbed by the magnetized electrons of the background plasma, leading to the formation of non-Maxwellian electron tails. When entering the cold background plasma, these hot electrons, in turn, drive high frequency Langmuir oscillations with omega approximately equal to omega (pe) up to the high level W(L)/n(0)T(e) of about 0.00001-0.0001. The conversion of plasma waves into electromagnetic waves is caused by the induced scattering of plasma waves of ions or by merging of two Langmuir waves. The role of nonlinear processes is studied. The brightness temperature calculated from the theory, T(b) of about 10 to the 11th K, appears to be in very good agreement with observations.