Imaging of the Quiet Sun in the Frequency Range of 20-80 MHz

TL;DR

This paper presents high-resolution interferometric imaging of the quiet Sun at 20-80 MHz using LOFAR, revealing brightness temperature spectra, coronal sizes, and persistent dark regions, advancing understanding of solar radio emission in this frequency range.

Contribution

First high-quality interferometric imaging spectroscopy of the quiet Sun below 90 MHz, providing new insights into its brightness temperature spectrum and coronal structure.

Findings

Brightness temperature spectrum characterized across 20-80 MHz.

Identification of persistent dark coronal regions at these frequencies.

Comparison with bremsstrahlung models and previous observations.

Abstract

Radio emission of the quiet Sun is considered to be due to thermal bremsstrahlung emission of the hot solar atmosphere. The properties of the quiet Sun in the microwave band have been well studied, and they can be well described by the spectrum of bremsstrahlung emission. In the meter-wave and decameter-wave bands, properties of the quiet Sun have rarely been studied due to the instrumental limitations. In this work, we use the LOw Frequency ARray (LOFAR) telescope to perform high quality interferometric imaging spectroscopy observations of quiet Sun coronal emission at frequencies below 90~MHz. We present the brightness temperature spectrum, and size of the Sun in the frequency range of 20-80~MHz. We report on dark coronal regions with low brightness temperature that persist with frequency. The brightness temperature spectrum of the quiet Sun is discussed and compared with the bremsstrahlung emission of a coronal model and previous quiet Sun observations.