Letter to the Editor

Particle-in-cell simulations of shocks and band splitting of type II solar radio bursts

¹ Laboratory for Plasma Astrophysics, Faculty of Engineering, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan e-mail: sakaijun@eng.u-toyama.ac.jp
² Astronomical Institute, Academy of Sciences of the Czech Republic, v.v.i., Fričova 298, 251 65 Ondřejov, Czech Republic

Received: 25 September 2007
Accepted: 22 November 2007

Abstract

Aims.We investigate the emission process of electromagnetic waves from proton beams reflected by the front of a fast magnetosonic shock that propagates in a non-uniform density region, by changing the propagation angle with respect to a uniform magnetic field from 90° to 45°.

Methods.A two-dimensional, electromagnetic, relativistic particle-in-cell (PIC) code is used.

Results.Near the shock front, some protons are reflected and accelerated. The reflected protons can drag the background electrons to keep the charge neutrality, resulting in electron acceleration. Due to the accelerated electrons, the electrostatic waves (Z-modes in the oblique propagation) can be excited where the reflected protons are generated. It is found that for about 60° propagation, the extra-ordinary waves can be excited from the shock front with a double oscillating structure. These waves are excited both near the fundamental and second harmonic frequency region of the local plasma frequency. The second harmonic waves have a band splitting structure and the lower band is brighter than the upper band part. For 45° propagation, the fundamental frequency region has a band splitting structure.