Evidence of 10-100 TeV Electrons in Supernova Remnants

Analyses of the X-ray data of the five young shell-type supernova remnants Cas A, Kepler, Tycho, SN 1006, and RCW 86 suggest that some of the X-ray emission of these sources is non-thermal. This non-thermal emission is qualitatively consistent with models of the broad-band (radio-to-X-ray) synchrotron spectra of remnants and does not seem to be consistent with other non-thermal X-ray emission processes. If this emission is produced by synchrotron radiation, the radio-to-X-ray synchrotron spectra imply that the electron spectra have differential spectral indices of about 2.2 and exponential cut offs at energies ~ 10 TeV. If the remnants also accelerate cosmic-ray nuclei, the total energies of the cosmic rays in the remnants are estimated to be ~ 1-5 X 10^49 erg. Therefore, the shapes of the cosmic-ray electron spectra, the maximum energies of the cosmic-ray electrons, and the total cosmic-ray energies of the five young remnants seem to be consistent with the idea that Galactic cosmic rays are predominantly accelerated in the shocks of supernova remnants.