Generation of a secondary shock wave during the oblique collision between a current sheet and a fast magnetosonic shock wave

Abstract

Aims. We investigate what happens when a fast magnetosonic shock wave associated with a coronal mass ejection (CME) collides obliquely with a coronal streamer with a stable current sheet. Methods. A two-dimensional relativistic and fully electromagnetic Particle-In-Cell (PIC) code is used. Results. It is shown that the fast magnetosonic shock with initial Alfven Mach $M_{\rm A}=5.6$ compresses the current sheet, resulting in strong deformation of the current sheet. In the later stage a secondary fast magnetosonic shock wave can be generated almost perpendicular to the current sheet, and it propagates away to the opposite side of the original shock. This newly generated shock wave may emit a type II radio burst. The simulation results may be applied to a split of electromagnetic wave emissions when a shock wave associated with CMEs collides obliquely with a coronal streamer. For weak initial Alfven Mach $M_{\rm A}=2.8$, a secondary shock wave does not appear, while the current sheet can be deformed and become unstable for tearing-like modes associated with magnetic reconnection.