Modeling Metric Gyrosynchrotron Radio Emission From the Quiet Solar Corona

TL;DR

This study models the potential contribution of gyrosynchrotron emission to the quiet Sun's radio signals at low frequencies, using MHD simulations and comparing results with LOFAR observations to better understand coronal magnetic fields and electron populations.

Contribution

It introduces a method to estimate gyrosynchrotron emission in the quiet Sun using MHD models and compares it with observations, highlighting its significance at low radio frequencies.

Findings

Gyrosynchrotron emission may significantly contribute to quiet Sun radio signals.

Model results help explain brightness variations in decametric coronal hole emissions.

The study constrains coronal magnetic field measurements using radio data.

Abstract

The radio emission of the quiet Sun in the metric and decametric bands has not been well studied historically due to limitations of existing instruments. It is nominally dominated by thermal brehmsstrahlung of the solar corona, but may also include significant gyrosynchrotron emission, usually assumed to be weak under quiet conditions. In this work, we investigate the expected gyrosynchrotron contribution to solar radio emission in the lowest radio frequencies observable by ground instruments, for different regions of the low and middle corona. We approximate the coronal conditions by a synoptic magnetohydrodynamic (MHD) model. The thermal emission is estimated from a forward model based on the simulated corona. We calculate the expected gyrosynchrotron emission with the Fast Gyrosynchrotron Codes framework by Fleishman & Kuznetsov (2010). The model emissions of different coronal regions are compared with quiet-time observations between 20-90 MHz by the LOw Frequency ARray (LOFAR) radio telescope. The contribution of gyrosynchrotron radiation to low frequency solar radio emission may shed light on effects such as the hitherto unexplained brightness variation observed in decametric coronal hole emission, and help constrain measurements of the coronal magnetic fields. It can also improve our understanding of electron populations in the middle corona and their relation to the formation of the solar wind.