Acceleration, magnetic fluctuations, and cross-field transport of energetic electrons in a solar flare loop

Kontar, E.P. , Hannah, I.G. and Bian, N.H. (2011) Acceleration, magnetic fluctuations, and cross-field transport of energetic electrons in a solar flare loop. Astrophysical Journal Letters, 730, (doi: 10.1088/2041-8205/730/2/L22)

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Plasma turbulence is thought to be associated with various physical processes involved in solar flares, including magnetic reconnection, particle acceleration, and transport. Using RHESSI observations and the X-ray visibility analysis, we determine the spatial and spectral distributions of energetic electrons for a flare (GOES M3.7 class, 2002 April 14, 23:55 UT), which was previously found to be consistent with a reconnection scenario. It is demonstrated that because of the high density plasma in the loop, electrons have to be continuously accelerated about the loop apex of length ~2 × 109 cm and width ~7 × 108 cm. Energy-dependent transport of tens of keV electrons is observed to occur both along and across the guiding magnetic field of the loop. We show that the cross-field transport is consistent with the presence of magnetic turbulence in the loop, where electrons are accelerated, and estimate the magnitude of the field line diffusion coefficient for different phases of the flare. The energy density of magnetic fluctuations is calculated for given magnetic field correlation lengths and is larger than the energy density of the non-thermal electrons. The level of magnetic fluctuations peaks when the largest number of electrons is accelerated and is below detectability or absent at the decay phase. These hard X-ray observations provide the first observational evidence that magnetic turbulence governs the evolution of energetic electrons in a dense flaring loop and is suggestive of their turbulent acceleration.

Item Type:Articles (Letter)
Additional Information:L22
Keywords:Sun: activity, Sun: flares, Sun: particle emission, Sun: X-rays, gamma rays
Glasgow Author(s) Enlighten ID:Bian, Dr Nicolas Horace and Hannah, Dr Iain and Kontar, Professor Eduard
Authors: Kontar, E.P., Hannah, I.G., and Bian, N.H.
Subjects:Q Science > QB Astronomy
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Astrophysical Journal Letters
ISSN (Online):2041-8213
Published Online:07 March 2011
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