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Title: Cosmic ray acceleration at perpendicular shocks in supernova remnants

Supernova remnants (SNRs) are believed to accelerate particles up to high energies through the mechanism of diffusive shock acceleration (DSA). Except for direct plasma simulations, all modeling efforts must rely on a given form of the diffusion coefficient, a key parameter that embodies the interactions of energetic charged particles with magnetic turbulence. The so-called Bohm limit is commonly employed. In this paper, we revisit the question of acceleration at perpendicular shocks, by employing a realistic model of perpendicular diffusion. Our coefficient reduces to a power law in momentum for low momenta (of index α), but becomes independent of the particle momentum at high momenta (reaching a constant value κ{sub ∞} above some characteristic momentum p {sub c}). We first provide simple analytical expressions of the maximum momentum that can be reached at a given time with this coefficient. Then we perform time-dependent numerical simulations to investigate the shape of the particle distribution that can be obtained when the particle pressure back-reacts on the flow. We observe that for a given index α and injection level, the shock modifications are similar for different possible values of p {sub c}, whereas the particle spectra differ markedly. Of particular interest, low values ofmore » p {sub c} tend to remove the concavity once thought to be typical of non-linear DSA, and result in steep spectra, as required by recent high-energy observations of Galactic SNRs.« less
Authors:
; ; ;  [1] ;  [2] ;  [3]
  1. Department of Physics and Astronomy, University of Manitoba, Winnipeg, MB, R3T 2N2 (Canada)
  2. Harvard University, 60 Garden Street, Cambridge, MA 02138 (United States)
  3. School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455 (United States)
Publication Date:
OSTI Identifier:
22365072
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 792; 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; CHARGED PARTICLES; COMPUTERIZED SIMULATION; COSMIC RADIATION; DIFFUSION; DISTRIBUTION; GALAXIES; INJECTION; INTERACTIONS; MODIFICATIONS; NONLINEAR PROBLEMS; PLASMA SIMULATION; SPECTRA; SUPERNOVA REMNANTS; TIME DEPENDENCE; TURBULENCE