On the variation of solar flare coronal x-ray source sizes with energy

Abstract

Observations with {\em RHESSI} have enabled the detailed study of the structure of dense hard X-ray coronal sources in solar flares. The variation of source extent with electron energy has been discussed in the context of streaming of non-thermal particles in a one-dimensional cold-target model, and the results used to constrain both the physical extent of, and density within, the electron acceleration region. Here we extend this investigation to a more physically realistic model of electron transport that takes into account the finite temperature of the ambient plasma, the initial pitch-angle distribution of the accelerated electrons, and the effects of collisional pitch-angle scattering. The finite temperature results in the thermal diffusion of electrons, that leads to the observationally-inferred value of the acceleration region volume being an overestimate of its true value. The different directions of the electron trajectories, a consequence of both the non-zero injection pitch-angle and scattering within the target, cause the projected propagation distance parallel to the guiding magnetic field to be reduced, so that a one-dimensional interpretation can overestimate the actual density by a factor of up to $\sim 6$. The implications of these results for the determination of acceleration region properties (specific acceleration rate, filling factor, etc.) are discussed.

45 pages, 9 figures, accepted for publication in ApJ

References in corpus (4)

• Stereoscopic electron spectroscopy of solar hard X-ray flares with a single spacecraft
• Hard X-ray Spectra and Positions of Solar Flares observed by RHESSI: photospheric albedo, directivity and electron spectra
• Radio Spectral Evolution of an X-ray Poor Impulsive Solar Flare: Implications for Plasma Heating and Electron Acceleration
• Footpoint versus loop-top hard X-ray emission sources in solar flares

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• A Fokker-Planck Framework for Studying the Diffusion of Radio Burst Waves in the Solar Corona
• Electron distribution and energy release in magnetic reconnection outflow regions during the pre-impulsive phase of a solar flare
• Particle acceleration with anomalous pitch angle scattering in 2D MHD reconnection simulations
• Spectral and Imaging Diagnostics of Spatially-Extended Turbulent Electron Acceleration and Transport in Solar Flares
• The efficiency of electron acceleration during the impulsive phase of a solar flare
• The Micro Solar Flare Apparutus (MiSolFA) Instrument Concept
• Flare-accelerated Electrons in the Kappa Distribution from X-Ray Spectra with the Warm-Target Model
• Time-dependent Turbulent Electron Acceleration and Transport in Solar Flares