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Title: The effect of stochastic re-acceleration on the energy spectrum of shock-accelerated protons

The energy spectra of particles in gradual solar energetic particle (SEP) events do not always have a power-law form attributed to the diffusive shock acceleration mechanism. In particular, the observed spectra in major SEP events can take the form of a broken (double) power law. In this paper, we study the effect of a process that can modify the power-law spectral form produced by the diffusive shock acceleration: the stochastic re-acceleration of energetic protons by enhanced Alfvénic turbulence in the downstream region of a shock wave. There are arguments suggesting that this process can be important when the shock propagates in the corona. We consider a coronal magnetic loop traversed by a shock and perform Monte Carlo simulations of interactions of shock-accelerated protons with Alfvén waves in the loop. The wave-particle interactions are treated self-consistently, so the finiteness of the available turbulent energy is taken into account. The initial energy spectrum of particles is taken to be a power law. The simulations reveal that the stochastic re-acceleration leads either to the formation of a spectrum that is described in a wide energy range by a power law (although the resulting power-law index is different from the initial one) or tomore » a broken power-law spectrum. The resulting spectral form is determined by the ratio of the energy density of shock-accelerated protons to the wave energy density in the shock's downstream region.« less
Authors:
;  [1] ;  [2]
  1. Department of Physics, University of Helsinki, P.O. Box 64, Helsinki FI-00014 (Finland)
  2. Sodankylä Geophysical Observatory (Oulu Unit), University of Oulu, Oulu FI-90014 (Finland)
Publication Date:
OSTI Identifier:
22365609
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 790; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCELERATION; ALFVEN WAVES; COMPUTERIZED SIMULATION; EMISSION; ENERGY DENSITY; ENERGY SPECTRA; MASS; MONTE CARLO METHOD; PARTICLE INTERACTIONS; PROTONS; SHOCK WAVES; STOCHASTIC PROCESSES; SUN; TURBULENCE