3D simulations of gyrosynchrotron emission from mildly anisotropic nonuniform electron distributions in symmetric magnetic loops

TL;DR

This study uses 3D simulations to analyze how electron anisotropy and spatial distribution in magnetic loops influence solar microwave emission, aiding in better diagnostics of energetic electrons in solar flares.

Contribution

It introduces a systematic simulation approach combining new tools to explore the effects of electron anisotropy and inhomogeneity on gyrosynchrotron emission in solar magnetic loops.

Findings

Electron anisotropy affects emission near footpoints and depends on loop orientation.

Spatial concentration of electrons shifts radio brightness peaks, reducing anisotropy effects.

Intermediate frequency spectra are highly sensitive to electron anisotropy and magnetic field nonuniformity.

Abstract

Microwave emission of solar flares is formed primarily by incoherent gyrosynchrotron radiation generated by accelerated electrons in coronal magnetic loops. The resulting emission depends on many factors, including pitch-angle distribution of the emitting electrons and the source geometry. In this work, we perform systematic simulations of solar microwave emission using recently developed tools (GS Simulator and fast gyrosynchrotron codes) capable of simulating maps of radio brightness and polarization as well as spatially resolved emission spectra. A 3D model of a symmetric dipole magnetic loop is used. We compare the emission from isotropic and anisotropic (of loss-cone type) electron distributions. We also investigate effects caused by inhomogeneous distribution of the emitting particles along the loop. It is found that effect of the adopted moderate electron anisotropy is the most pronounced near the footpoints and it also depends strongly on the loop orientation. Concentration of the emitting particles at the loop top results in a corresponding spatial shift of the radio brightness peak, thus reducing effects of the anisotropy. The high-frequency (around 50 GHz) emission spectral index is specified mainly by the energy spectrum of the emitting electrons; however, at intermediate frequencies (around 10-20 GHz), the spectrum shape is strongly dependent on the electron anisotropy, spatial distribution, and magnetic field nonuniformity. The implications of the obtained results for the diagnostics of the energetic electrons in solar flares are discussed.