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Durham University

Department of Physics

Staff profile

Publication details for Prof Sir Arnold Wolfendale

Erlykin, AD & Wolfendale, AW (2002). Supernova remnants and the origin of cosmic radiation: evidence fromlow-energy gamma rays. Journal Of Physics G-nuclear And Particle Physics 28(9): 2329-2348.
  • Publication type: Journal Article
  • ISSN/ISBN: 0954-3899
  • Keywords: INTERSTELLAR-MEDIUM; EGRET OBSERVATIONS; EMISSION; ACCELERATION;GALAXY; SPECTRUM; RADIO

Author(s) from Durham

Abstract

Our model, in which cosmic rays are accelerated by shocks in supernova
remnants (SNR) and then propagate by diffusion through the galaxy, has
been developed and applied to the case of the low-energy (Egamma less
than or equal to 10 GeV) diffuse gamma ray background. Attention is
given to the well-known 'GeV-excess' problem, i.e. the gamma ray
spectrum from the inner galaxy is flatter (and in the outer galaxy is
correspondingly steeper) in the range 1-10 GeV, than would have been
expected on the basis of gamma rays coming from the interactions of the
cosmic rays observed locally with gas and radiation fields. Attention
is also given to the related problem of the 'cosmic ray gradient', i.e.
the dependence of the low-energy cosmic ray intensity on galactocentric
distance; the gradient being deduced from the distribution of >0.1 GeV
gamma rays which is flatter than the known SNR distribution.
We argue that both problems can be solved in the framework of the
conception that SN explosions are the source of the turbulence in the
galactic disk leading to a radial dependence of the form of the
turbulence spectrum. We contend that the propagation of cosmic rays
through the turbulent interstellar medium (ISM) is governed by the
so-called anomalous diffusion. This form of diffusion leads to a
flatter energy spectrum of cosmic rays in the inner galaxy and a
steeper spectrum in the outer galaxy. Anomalous diffusion reduces also
the radial gradient of GeV cosmic rays in the inner galaxy; for the
outer galaxy we invoke re-entry of cosmic rays from the halo.
In the halo, where there are no SNR, the turbulence is driven by cosmic
rays themselves and their energy spectrum has to be as steep as in the
outer galaxy.