Spectral and Imaging Diagnostics of Spatially-Extended Turbulent Electron Acceleration and Transport in Solar Flares

Abstract

Solar flares are efficient particle accelerators with a large fraction of released magnetic energy (10-50%) converted into energetic particles such as hard X-ray producing electrons. This energy transfer process is not well constrained, with competing theories regarding the acceleration mechanism(s), including MHD turbulence. We perform a detailed parameter study examining how various properties of the acceleration region, including its spatial extent and the spatial distribution of turbulence, affect the observed electron properties, such as those routinely determined from X-ray imaging and spectroscopy. Here, a time-independent Fokker-Planck equation is used to describe the acceleration and transport of flare electrons through a coronal plasma of finite temperature. Motivated by recent non-thermal line broadening observations that suggested extended regions of turbulence in coronal loops, an extended turbulent acceleration region is incorporated into the model. We produce outputs for the density weighted electron flux, a quantity directly related to observed X-rays, modelled in energy and space from the corona to chromosphere. We find that by combining several spectral and imaging diagnostics (such as spectral index differences or ratios, energy or spatial-dependent flux ratios, and electron depths into the chromosphere) the acceleration properties, including the timescale and velocity dependence, can be constrained alongside the spatial properties. Our diagnostics provide a foundation for constraining the properties of acceleration in an individual flare from X-ray imaging spectroscopy alone, and can be applied to past, current and future observations including those from RHESSI and Solar Orbiter.

ApJ Accepted

References in corpus (6)

• The Solar Orbiter mission -- Science overview
• Relations between concurrent hard X-ray sources in solar flares
• A Hitch-hiker's Guide to Stochastic Differential Equations: Solution Methods for Energetic Particle Transport in Space Physics and Astrophysics
• On the variation of solar flare coronal x-ray source sizes with energy
• Determination of the total accelerated electron rate and power using solar flare hard X-ray spectra
• Spatio-temporal energy partitioning in a non-thermally dominated two-loop solar flare

Cited by in corpus (3)

• The efficiency of electron acceleration during the impulsive phase of a solar flare
• Time-dependent Turbulent Electron Acceleration and Transport in Solar Flares
• Energy-Containing Electrons in Solar Flares: Improving Hard X-Ray and EUV Diagnostics