Synthetic radio views on simulated solar flux ropes

TL;DR

This study creates synthetic radio images of simulated solar flux ropes using MHD models, revealing how magnetic field strength and structure influence radio emission features, including free-free and gyroresonance signals, with implications for solar observations.

Contribution

It introduces a method to produce synthetic radio views of flux ropes from MHD simulations, enabling detailed analysis of radio emission mechanisms in different magnetic conditions.

Findings

Flux ropes with up to 100 G show optically thin free-free emission.

Strong fields up to 680 G produce detectable gyroresonance emission at frequencies up to 7 GHz.

Synthetic views of embedded filaments resemble actual observations, especially at the limb.

Abstract

In this paper, we produce synthetic radio views on simulated flux ropes in the solar corona, where finite-beta magnetohydrodynamic (MHD) simulations serve to mimic the flux rope formation stages, as well as their stable endstates. These endstates represent twisted flux ropes where balancing Lorentz forces, gravity and pressure gradients determine the full thermodynamic variation throughout the flux rope. The obtained models are needed to quantify radiative transfer in radio bands, and allow us to contrast weak to strong magnetic field conditions. Field strengths of up to 100 G in the flux rope yield the radio views dominated by optically thin free-free emission. The forming flux rope shows clear morphological changes in its emission structure as it deforms from an arcade to a flux rope, both on disk and at the limb. For an active region filament channel with a field strength of up to 680 G in the flux rope, gyroresonance emission (from the third-fourth gyrolayers) can be detected and even dominates over free-free emission at the frequencies of up to 7 GHz. Finally, we also show synthetic views on a simulated filament embedded within a (weak-field) flux rope, resulting from an energetically consistent MHD simulation. For this filament, synthetic views at the limb show clear similarities with actual observations, and the transition from optically thick (below 10 GHz) to optically thin emission can be reproduced. On the disk, its dimension and temperature conditions are as yet not realistic enough to yield the observed radio brightness depressions.