Simulations of Gyrosynchrotron Microwave Emission from an Oscillating 3D Magnetic Loop

TL;DR

This study simulates gyrosynchrotron microwave emission from an oscillating 3D magnetic loop to identify observable signatures of MHD oscillations, aiding interpretation of solar flare radio observations.

Contribution

It introduces a 3D modeling approach for gyrosynchrotron emission from oscillating magnetic loops, considering various parameters and viewing angles, to better understand MHD oscillation signatures.

Findings

Intensity oscillations are synchronous at all frequencies in low-density models.

In high-density models, low-frequency emission oscillates in anti-phase with high-frequency emission.

Oscillation patterns depend on loop orientation and magnetic field sign changes.

Abstract

Radio observations of solar flares often reveal various periodic or quasi-periodic oscillations. Most likely, these oscillations are caused by magnetohydrodynamic (MHD) oscillations of flaring loops which modulate the emission. Interpretation of the observations requires comparing them with simulations. We simulate the gyrosynchrotron radio emission from a semi-circular (toroidal-shaped) magnetic loop containing sausage-mode MHD oscillations. The aim is to detect the observable signatures specific to the considered MHD mode and to study their dependence on the various source parameters. The MHD waves are simulated using a linear three-dimensional model of a magnetized plasma cylinder; both standing and propagating waves are considered. The curved loop is formed by replicating the MHD solutions along the plasma cylinder and bending the cylinder; this model allows us to study the effect of varying the viewing angle along the loop. The radio emission is simulated using a three-dimensional model and its spatial and temporal variations are analyzed. We consider several loop orientations and different parameters of the magnetic field, plasma, and energetic electrons in the loop. In the model with low plasma density, the intensity oscillations at all frequencies are synchronous (with the exception of a narrow spectral region below the spectral peak). In the model with high plasma density, the emission at low frequencies (where the Razin effect is important) oscillates in anti-phase with the emissions at higher frequencies. The oscillations at high and low frequencies are more pronounced in different parts of the loop (depending on the loop orientation). The layers where the line-of-sight component of the magnetic field changes sign can produce additional peculiarities in the oscillation patterns.