Turbulent pitch-angle scattering and diffusive transport of hard x-ray-producing electrons in flaring coronal loops

Kontar, E.P. , Bian, N.H., Emslie, A.G. and Vilmer, N. (2014) Turbulent pitch-angle scattering and diffusive transport of hard x-ray-producing electrons in flaring coronal loops. Astrophysical Journal, 780(2), p. 176. (doi:10.1088/0004-637X/780/2/176)

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Recent observations from RHESSI have revealed that the number of non-thermal electrons in the coronal part of a flaring loop can exceed the number of electrons required to explain the hard X-ray-emitting footpoints of the same flaring loop. Such sources cannot, therefore, be interpreted on the basis of the standard collisional transport model, in which electrons stream along the loop while losing their energy through collisions with the ambient plasma; additional physical processes, to either trap or scatter the energetic electrons, are required. Motivated by this and other observations that suggest that high-energy electrons are confined to the coronal region of the source, we consider turbulent pitch-angle scattering of fast electrons off low-frequency magnetic fluctuations as a confinement mechanism, modeled as a spatial diffusion parallel to the mean magnetic field. In general, turbulent scattering leads to a reduction of the collisional stopping distance of non-thermal electrons along the loop, and hence to an enhancement of the coronal hard X-ray source relative to the footpoints. The variation of source size L with electron energy E becomes weaker than the quadratic behavior pertinent to collisional transport, with the slope of L(E) depending directly on the mean free path λ associated with the non-collisional scattering mechanism. Comparing the predictions of the model with observations, we find that λ ~ (108-109) cm for ~30 keV, less than the length of a typical flaring loop and smaller than, or comparable to, the size of the electron acceleration region.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Kontar, Professor Eduard and Bian, Dr Nicolas Horace
Authors: Kontar, E.P., Bian, N.H., Emslie, A.G., and Vilmer, N.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Astrophysical Journal
ISSN (Online):1538-4357
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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
542081Rolling Programme in Solar and Plasma AstrophysicsLyndsay FletcherScience & Technologies Facilities Council (STFC)ST/I001808/1P&A - PHYSICS & ASTRONOMY