The Relationship Between Solar Radio and Hard X-ray Emission

Abstract

This review discusses the complementary relationship between radio and hard X-ray observations of the Sun using primarily results from the era of the Reuven Ramaty High Energy Solar Spectroscopic Imager satellite. A primary focus of joint radio and hard X-ray studies of solar flares uses observations of nonthermal gyrosynchrotron emission at radio wavelengths and bremsstrahlung hard X-rays to study the properties of electrons accelerated in the main flare site, since it is well established that these two emissions show very similar temporal behavior. A quantitative prescription is given for comparing the electron energy distributions derived separately from the two wavelength ranges: this is an important application with the potential for measuring the magnetic field strength in the flaring region, and reveals significant differences between the electrons in different energy ranges. Examples of the use of simultaneous data from the two wavelength ranges to derive physical conditions are then discussed, including the case of microflares, and the comparison of images at radio and hard X-ray wavelengths is presented. There have been puzzling results obtained from observations of solar flares at millimeter and submillimeter wavelengths, and the comparison of these results with corresponding hard X-ray data is presented. Finally, the review discusses the association of hard X-ray releases with radio emission at decimeter and meter wavelengths, which is dominated by plasma emission (at lower frequencies) and electron cyclotron maser emission (at higher frequencies), both coherent emission mechanisms that require small numbers of energetic electrons. These comparisons show broad general associations but detailed correspondence remains more elusive.

This is an article prepared for a monograph on the physics of solar flares, inspired by RHESSI observations. The chapters appear as individual articles in Space Science Reviews (2011)

References in corpus (6)

• RHESSI Line and Continuum Observations of Super-hot Flare Plasma
• Broadband Quasi-Periodic Radio and X-ray Pulsations in a Solar Flare
• Comparative Analysis of Non-thermal Emissions and Study of Electron Transport in a Solar Flare
• The x-ray detectability of electron beams escaping from the sun
• Sub-terahertz, microwaves and high energy emissions during the December 6, 2006 flare, at 18:40 UT
• Eruptions of Magnetic Ropes in Two Homologous Solar Events on 2002 June 1 and 2: a Key to Understanding of an Enigmatic Flare

Cited by in corpus (57)

• An Observational Overview of Solar Flares
• Implications of X-ray Observations for Electron Acceleration and Propagation in Solar Flares
• The Magnetic Field in the Solar Atmosphere
• Slipping Magnetic Reconnection, Chromospheric Evaporation, Implosion, and Precursors in the 2014 September 10 X1.6-Class Solar Flare
• 3D Radio and X-Ray Modeling and Data Analysis Software: Revealing Flare Complexity
• Electron Power-Law Spectra in Solar and Space Plasmas
• Simultaneous IRIS and Hinode/EIS observations and modelling of the 27 October 2014 X 2.0 class flare
• Tracing Electron Beams in the Sun's Corona with Radio Dynamic Imaging Spectroscopy
• Magnetic-Island Contraction and Particle Acceleration in Simulated Eruptive Solar Flares
• Non-Equilibrium Processes in the Solar Corona, Transition Region, Flares, and Solar Wind \textit{(Invited Review)}
• Estimation of a Coronal Mass Ejection Magnetic Field Strength using Radio Observations of Gyrosynchrotron Radiation
• Solar Physics with the Square Kilometre Array
• Large-scale contraction and subsequent disruption of coronal loops during various phases of the M6.2 flare associated with the confined flux rope eruption
• Quasi-Periodic Particle Acceleration in a Solar Flare
• Type III Solar Radio Burst Source Region Splitting Due to a Quasi-Separatrix Layer
• The Second Arecibo Search for 5 GHz Radio Flares from Ultracool Dwarfs
• Energetic Electron Distribution of the Coronal Acceleration Region: First results from Joint Microwave and Hard X-ray Imaging Spectroscopy
• Spatio-temporal dynamics of sources of hard X-ray pulsations in solar flares
• Thermal to Nonthermal Energy Partition at the Early Rise Phase of Solar Flares
• Three-dimensional Forward-fit Modeling of the Hard X-Ray and the Microwave Emissions of the 2015 June 22 M6.5 Flare
• Numerical Modeling of Energetic Electron Acceleration, Transport, and Emission in Solar Flares: Connecting Loop-top and Footpoint Hard X-Ray Sources
• Mottled protoplanetary disk ionization by magnetically-channeled T Tauri star energetic particles
• Microwave imaging of a hot flux rope structure during the pre-impulsive stage of an eruptive M7.7 solar flare
• Localising pulsations in the hard X-ray and microwave emission of an X-class flare
• Radio, Hard X-Ray, and Gamma-Ray Emissions Associated with a Far-Side Solar Event
• Pre-flare processes, flux rope activation, large-scale eruption and associated X-class flare from the active region NOAA 11875
• Is Cyclotron Maser Emission in Solar Flares Driven by a Horseshoe Distribution?
• Double Coronal X-ray and Microwave Sources Associated With A Magnetic Breakout Solar Eruption
• Connecting solar flare hard X-ray spectra to in situ electron spectra. A comparison of RHESSI and STEREO/SEPT observations
• The first flare observation with a new solar microwave spectrometer working in 35-40 GHz
• The Rise of ROME. I. A Multiwavelength Analysis of the Star-Planet Interaction in the HD 189733 System
• Two-stage energy release process of a confined flare with double HXR peaks
• Radio-flaring Ultracool Dwarf Population Synthesis
• Bridging High-Density, Electron Beam Coronal Transport and Deep Chromospheric Heating in Stellar Flares
• Harmonic elctron-cyclotron maser emissions driven by energetic electrons of the horseshoe distribution with application to solar radio spikes
• Validation Of The Coronal Thick Target Source Model
• A burst with double radio spectrum observed up to 212 GHz
• Relations between strong high-frequency microwave bursts and proton events
• A solar flare driven by thermal conduction observed in mid-infrared
• Gyrosynchrotron emission generated by nonthermal electrons with energy spectra of a broken power law
• Generic model for magnetic explosions applied to solar flares
• Performance of Major Flare Watches from the Max Millennium Program (2001-2010)
• Radio and X-ray Observations of Short-lived Episodes of Electron Acceleration in a Solar Microflare
• A model of double coronal hard X-ray sources in solar flares
• Multiple electron acceleration instances during a series of solar microflares observed simultaneously at X-rays and microwaves
• The efficiency of electron acceleration during the impulsive phase of a solar flare
• Multiwavelength Stereoscopic Observation of the May 1, 2013 Solar Flare and CME
• Sources of Quasi-Periodic Pulses in the 18 August 2012 Flare
• Decimetric emission 500${}^{\prime \prime }$ away from a flaring Site: Possible scenarios from $\text{GMRT}$ solar radio observations
• Global energetics of solar powerful events on 6 September 2017
• Onset of Electron Acceleration in a Flare Loop
• Implications for additional plasma heating driving the extreme-ultraviolet late phase of a solar flare with microwave imaging spectroscopy
• Twin Null-Point-Associated Major Eruptive Three-Ribbon Flares with Unusual Microwave Spectra
• Solar Gamma-Ray Evidence for a Distinct Population of $>$ 1 MeV Flare-Accelerated Electrons
• Non-thermal electron energization during the impulsive phase of an X9.3 flare revealed by Insight-HXMT
• First Detailed MeerKAT Imaging Spectroscopy of a Solar Flare
• Single-Mode Wave Decay