It has long been thought (though there was no direct proof) that cosmic rays up to a certain energy range are accelerated in the shocks of supernova remnants. There are many good reasons to think this, but it has not been until very recently that evidence supporting this hypothesis has been found. X-ray spectra of the remnant from SN 1006 taken by ASCA showed conclusively that the remnant was generating synchrotron radiation in its outer rims. The spectrum in the outer rims was a straight line while the spectrum of emission from the much fainter center showed thermal emission from a hot gas. The observations conflicted with other theories that had been used to explain SNR spectra up until this time.

Since synchrotron radiation arises from energetic particles moving in a magnetic field, the existence of a synchrotron spectrum means that there must be a magnetic field and a population of accelerated particles in or near the SNR. From the energy of the synchrotron emission and the estimated strength of the magnetic field we can calculate the energies of the polulation of accelerated particles. This value agrees with the energies of cosmic rays observed at Earth. In fact, the energy released by supernova explosions (and transfered into kinetic energy of the remnant) is more than enough to account for the observed cosmic rays. The conclusion is that most, if not all, of the cosmic rays in the Galaxy below a certain energy are accelerated in this way.

< SN1006: Saga of two spectra

by J. Allie Cliffe and Glenn Allen

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