New Insights from Imaging Spectroscopy of Solar Radio Emission

Abstract

Newly available high-resolution imaging of solar radio emission at many closely spaced frequencies and times provides new physical insight into the processes, structure, and dynamics of the solar atmosphere. The observational advances have spurred renewed interest in topics dating from the early days of solar radio astronomy and have led to considerable advances in our knowledge. Highlights of recent advances include the following: ▪ Quantitatively measuring the dynamic magnetic field strength, particle acceleration, and hot thermal plasma at the heart of solar flares and hinting at the processes that relate them. ▪ Resolving in space and time the energization and transport of electrons in a wide range of contexts. ▪ Mapping the magnetized thermal plasma structure of the solar chromosphere and corona over a substantial range of heights in active and quiet regions of the Sun. This review explains why solar radio imaging spectroscopy is so powerful, describes the body of recent results, and outlines the future work needed to fully realize its potential. The application of radio imaging spectroscopy to stars and planets is also briefly reviewed. Expected final online publication date for the Annual Review of Astronomy and Astrophysics, Volume 61 is August 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Fine Structure of Solar Metric Radio Bursts: ARTEMIS-IV/JLS and NRH Observations

“…This is due to the lack of instruments capable of providing both spectral and imaging data, with the exception of LOFAR; thus, most spectral imaging has been performed with spectra and images from different instruments with different characteristics. The situation is improving; however, with a number of spectral imaging instruments in operation or under development (See also the review by [180]):…”

Spectroscopic Imaging of the Sun with MeerKAT: Opening a New Frontier in Solar Physics

“…Since the discovery of solar radio emission (Reber 1944), the Sun has been studied in great detail in a wide range of frequencies spanning the range from a few kilohertz to several hundreds of gigahertz (e.g., Pick & Vilmer 2008;Gary 2023). Despite this long history of observations and studies, the Sun still harbors several mysteries.…”

A Joint Microwave and Hard X-Ray Study toward Understanding the Transport of Accelerated Electrons During an Eruptive Solar Flare

“…At the radio wavelengths, the signatures of nonthermal electrons are attributed to either coherent emission mechanisms, including the plasma emission and the electron cyclotron maser emission, or the nonthermal gyrosynchrotron emission. The coherent emissions are generally observed at frequencies 2 GHz, whereas nonthermal gyrosynchrotron emission is more common at higher frequencies (Bastian et al 1998;Nindos 2020;Gary 2023). The coherent emissions are extremely sensitive tracers of the nonthermal electrons and have been used in the past to trace electrons at or near their acceleration site(s) (Chen et al 2015(Chen et al , 2018 and to track their transport in the corona (e.g., Chen et al 2013;McCauley et al 2017;Mann et al 2018;Yu & Chen 2019) and in the heliosphere (e.g., Musset et al 2021;Badman et al 2022;Wang et al 2023).…”

“…However, these emissions involve highly nonlinear radiation processes and are also extremely sensitive to the details of the local plasma conditions and source electron distribution; hence, it remains challenging to invert the observations and quantify the nonthermal electron distribution. Nonthermal gyrosynchrotron emission, on the other hand, is an incoherent emission mechanism and can be used to provide quantitative constraints on the nonthermal electron population (see the reviews by Bastian et al 1998;Nindos 2020;Gary 2023). However, the nonthermal gyrosynchrotron emission is primarily sensitive to electrons having energies 100 keV (White et al 2011;Krucker et al 2020;Chen et al 2021).…”