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

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 themore » non-collisional scattering mechanism. Comparing the predictions of the model with observations, we find that λ ∼ (10{sup 8}-10{sup 9}) 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.« less
Authors:
;  [1] ;  [2] ;  [3]
  1. School of Physics and Astronomy, The University of Glasgow, G12 8QQ (United Kingdom)
  2. Department of Physics and Astronomy, Western Kentucky University, Bowling Green, KY 42101 (United States)
  3. LESIA Observatoire de Paris, CNRS, UPMC, Universite Paris Diderot, 5 place Jules Janssen, 92195 Meudon Cedex (France)
Publication Date:
OSTI Identifier:
22348206
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 780; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCELERATION; COMPARATIVE EVALUATIONS; DIFFUSION; DISTANCE; FLUCTUATIONS; GAMMA RADIATION; HARD X RADIATION; INCLINATION; KEV RANGE; MAGNETIC FIELDS; MEAN FREE PATH; PLASMA; REDUCTION; SCATTERING; STREAMS; SUN; TAIL ELECTRONS; TRANSPORT THEORY; TRAPS