Escaping the accelerator; how, when and in what numbers do cosmic rays get out of supernova remnants?

The escape of charged particles accelerated by diffusive shock acceleration from supernova remnants is shown to be a more complex process than normally appreciated. Using a box model it is shown that the high-energy end of the spectrum can exhibit spectral breaks even with no formal escape as a result of geometrical dilution and changing time-scales. It is pointed out that the bulk of the cosmic ray particles at lower energies must be produced and released in the late stages of the remnant's evolution whereas the high energy particles are produced early on; this may explain recent observations of slight compositional variations with energy. Escape resulting from ion-neutral friction in dense and partially ionized media is discussed briefly and some comments made on the use of so-called "free escape boundary conditions". Finally estimates are made of the total production spectrum integrated over the life of the remnant.

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