Energy Release and Particle Acceleration in Flares: Summary and Future Prospects

Abstract

RHESSI measurements relevant to the fundamental processes of energy release and particle acceleration in flares are summarized. RHESSI's precise measurements of hard X-ray continuum spectra enable model-independent deconvolution to obtain the parent electron spectrum. Taking into account the effects of albedo, these show that the low energy cut-off to the electron power-law spectrum is typically below tens of keV, confirming that the accelerated electrons contain a large fraction of the energy released in flares. RHESSI has detected a high coronal hard X-ray source that is filled with accelerated electrons whose energy density is comparable to the magnetic-field energy density. This suggests an efficient conversion of energy, previously stored in the magnetic field, into the bulk acceleration of electrons. A new, collisionless (Hall) magnetic reconnection process has been identified through theory and simulations, and directly observed in space and in the laboratory; it should occur in the solar corona as well, with a reconnection rate fast enough for the energy release in flares. The reconnection process could result in the formation of multiple elongated magnetic islands, that then collapse to bulk-accelerate the electrons, rapidly enough to produce the observed hard X-ray emissions. RHESSI's pioneering γ-ray line imaging of energetic ions, revealing footpoints straddling a flare loop arcade, has provided strong evidence that ion acceleration is also related to magnetic reconnection. Flare particle acceleration is shown to have a close relationship to impulsive Solar Energetic Particle (SEP) events observed in the interplanetary medium, and also to both fast coronal mass ejections and gradual SEP events.

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

References in corpus (13)

• An exceptionally bright flare from SGR1806-20 and the origins of short-duration gamma-ray bursts
• Impulsive phase flare energy transport by large-scale Alfven waves and the electron acceleration problem
• Electron Acceleration by Multi-Island Coalescence
• A catastrophe model for fast magnetic reconnection onset
• Double Coronal Hard and Soft X-ray Source Observed by RHESSI: Evidence for Magnetic Reconnection and Particle Acceleration in Solar Flares
• RHESSI Line and Continuum Observations of Super-hot Flare Plasma
• Compton backscattered and primary X-rays from solar flares: angle dependent Green's function correction for photospheric albedo
• Nonthermal Hard X-ray Emission and Iron Kalpha Emission from a Superflare on II Pegasi
• A Model for Spontaneous Onset of Fast Magnetic Reconnection
• Solar wind density turbulence and solar flare electron transport from the Sun to the Earth
• Low-energy cutoffs in electron spectra of solar flares: statistical survey
• Multi-wavelength analysis of high energy electrons in solar flares: a case study of August 20, 2002 flare
• Spectral Hardening of Large Solar Flares

Cited by in corpus (32)

• Nonthermally Dominated Electron Acceleration during Magnetic Reconnection in a Low-beta Plasma
• Electron Power-Law Spectra in Solar and Space Plasmas
• Particle acceleration and transport in reconnecting twisted loops in a stratified atmosphere
• Non-Equilibrium Processes in the Solar Corona, Transition Region, Flares, and Solar Wind \textit{(Invited Review)}
• A Very Bright, Very Hot, and Very Long Flaring Event from the M Dwarf Binary System DG CVn
• 3He-Rich Solar Energetic Particles in Helical Jets on the Sun
• Large-scale Compression Acceleration during Magnetic Reconnection in a Low-$\beta$ Plasma
• The First Focused Hard X-ray Images of the Sun with NuSTAR
• The Origin of Non-Maxwellian Solar Wind Electron Velocity Distribution Function: Connection to Nanoflares in the Solar Corona
• Evolution of the Solar Flare Energetic Electrons in the Inhomogeneous Inner Heliosphere
• Variations in emission from episodic plasmoid ejecta around black holes
• Radio Diagnostics of Electron Acceleration Sites During the Eruption of a Flux Rope in the Solar Corona
• The Effect of Thermal Pressure on Collisionless Magnetic Reconnection Rate
• Prospects of Detecting Non-thermal Protons in Solar Flares via Lyman Line Spectroscopy: Revisiting the Orrall-Zirker Effect
• Study of flare energy release using events with numerous type III-like bursts in microwaves
• Improved Type III solar radio burst detection using congruent deep learning models
• Cyclotron maser emission from power-law electrons with strong pitch-angle anisotropy
• Large solar energetic particle event that occurred on 2012 March 7 and its VDA analysis
• Improved modelling of SEP event onset within the WSA-Enlil-SEPMOD framework
• On-board GRB trigger algorithms of SVOM-GRM
• A Brief Review on Particle Acceleration in Multi-island Magnetic Reconnection
• Forecasting Solar Energetic Proton Integral Fluxes with Bi-Directional Long Short-Term Memory Neural Networks
• Microwave Signature of Relativistic Positrons in Solar Flares
• Observations of a Radio-quiet Solar Preflare
• Perspectives of current-layer diagnostics in solar flares
• Preferential acceleration of heavy ions in magnetic reconnection: Hybrid-kinetic simulations with electron inertia
• Three-dimensional Magnetic and Thermodynamic Structures of Solar Microflares
• In situ evidence of ion acceleration between consecutive reconnection jet fronts
• The effect of electron holes on cyclotron maser emission driven by horseshoe distributions
• Efficient Nonthermal Ion and Electron Acceleration Enabled by the Flux-Rope Kink Instability in 3D Nonrelativistic Magnetic Reconnection
• Always a Farm Boy
• X-ray fine structure of a limb solar flare revealed by Insight-HXMT, RHESSI and Fermi