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Durham University

Department of Physics

Staff profile

Publication details for Prof Sir Arnold Wolfendale

Erlykin, AD & Wolfendale, AW (2006). The nature of the 'knee' in the cosmic ray energy spectrum. Journal Of Physics G-nuclear And Particle Physics 32(1): 1-7.
  • Publication type: Journal Article
  • ISSN/ISBN: 0954-3899

Author(s) from Durham


In view of recent developments, attention is directed again at two
aspects of the well-known 'knee' in the cosmic ray energy spectrum at 3
PeV: the mass of the predominant particles at this energy and their
source. It is inevitable in a subject such as this that ideas-and
conclusions-evolve. Earlier, we had used a particular acceleration
model and the nature of the ISM in the local ISM to infer that the
particles are mainly oxygen nuclei; direct measurements, when
extrapolated (by at least a decade in energy), gave a similar result.
Initially, no specific source was identified. More recently, however,
we have specified the Monogem Ring supernova remnant as the likely
source; this is at just the right distance and age and the energies are
reasonable. Concerning the mass composition at the knee, a quantity
more difficult to determine, recent direct measurements, which extend
to higher energies than hitherto, show a likely flattening in the
spectrum above similar to 10(4) GeV/nucleon for He-nuclei, a flattening
which, if extrapolated to higher energies, would meet the measured
spectrum in the knee region. The other nuclei do not show this feature.
He-nuclei in the knee region would also be marginally more consistent
with KASCADE extensive air shower data, although there are serious
problems with EAS mass estimates in that experiment. Concerning the
acceleration, recent models applied to the Monogem Ring SNR allow a
satisfactory explanation in terms of either oxygen or helium, but with
the latter being a distinct possibility and perhaps more likely.