AAS 201st Meeting, January, 2003
Session 94. HEAD I: Cosmic Ray Physics in the 21st Century
Special, Wednesday, January 8, 2003, 10:00-11:30am, 6AB

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[94.02] Cosmic Rays at the Edge

S. Simon (University of Chicago)

A first glance at the energy spectrum of the intensities of cosmic rays produces the impression of a rather featureless power-law which extends over at least twelve decades in energy and over thirty(!) decades in intensity. There has yet to be a unified picture which explains this radiation. A closer look at this spectrum reveals a small steeping or `knee' near PeV energies. The origin of this feature is unknown, but it is thought to be connected to the maximum energies which can be provided by diffusive shock acceleration in supernovae remnants. This knee is therefore at the edge of our conventional understanding of cosmic ray origin. The extent to which the composition of cosmic rays is known in this region and what this could mean will be discussed. Almost all progress in understanding cosmic rays at lower energies has stemmed from the reliable determination of their composition. Some exploration will also be made of extending our conventional ideas about low energy cosmic rays to energies near the `edge'.

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