Energy Spectral Property in an Isolated CME-driven Shock

TL;DR

This study uses Monte Carlo simulations to analyze energy spectral breaks in CME-driven shocks, suggesting that such breaks are due to an energy cutoff rather than the highest energy tails exceeding the break range.

Contribution

The paper demonstrates that energy spectral breaks in isolated CME-driven shocks are likely caused by a spectral cutoff, not by the highest energy tails surpassing the break energy.

Findings

Energy tails saturate near 5MeV, below the break range.

No highest energy tails beyond the break energy range were found.

Spectral breaks may require shock interactions for formation.

Abstract

Observations from multiple spacecraft show that there are energy spectral "breaks" at 1-10MeV in some large CME-driven shocks. However, numerical models can hardly simulate this property due to high computational expense. The present paper focuses on analyzing these energy spectral "breaks" by Monte Carlo particle simulations of an isolated CME-driven shock. Taking the Dec 14 2006 CME-driven shock as an example, we investigate the formation of this energy spectral property. For this purpose, we apply different values for the scattering time in our isolated shock model to obtain the highest energy "tails", which can potentially exceed the "break" energy range. However, we have not found the highest energy "tails" beyond the "break" energy range, but instead find that the highest energy "tails" reach saturation near the range of energy at 5MeV. So, we believe that there exists an energy spectral "cut off" in an isolated shock. If there is no interaction with another shock, there would not be formation of the energy spectral "break" property.