Emission of Type II Radio Bursts - Single-Beam versus Two-Beam Scenario

TL;DR

This study uses advanced simulations to investigate the electron beam configurations responsible for Type II radio burst emissions, finding that two counterpropagating beams are necessary for wave interactions that produce observable radio waves.

Contribution

It demonstrates through simulations that two-beam electron configurations are required for Type II radio burst emission, challenging the single-beam assumption.

Findings

Two-beam scenario shows electromagnetic emission at fundamental and harmonic frequencies.

Single-beam scenario does not produce detectable wave signatures.

Results support the two-beam model as essential for Type II radio burst generation.

Abstract

The foreshock region of a CME shock front, where shock accelerated electrons form a beam population in the otherwise quiescent plasma is generally assumed to be the source region of type II radio bursts. Nonlinear wave interaction of electrostatic waves excited by the beamed electrons are the prime candidates for the radio waves' emission. To address the question whether a single, or two counterpropagating beam populations are a requirement for this process, we have conducted 2.5D particle in cell simulations using the fully relativistic ACRONYM code. Results show indications of three wave interaction leading to electromagnetic emission at the fundamental and harmonic frequency for the two-beam case. For the single-beam case, no such signatures were detectable.