| This thesis contains observational studies of shell-type supernova remnants (SNRs), primarily using the ROSAT and ASCA X-ray observatories. These results include: (1) evidence for turbulent magnetic field amplification in the young supernova remnant Cas A, (2) upper limits on the maximum energy which SNRs accelerate cosmic rays.; (1) When inhomogeneous absorption is taken into account, the soft X-ray and radio morphologies of the young SNR, Cas A, are strikingly similar. We conclude from the slope of the X-ray/radio surface brightness correlation, that the density of gas (traced by the X-ray) is proportional to the square of the magnetic field (traced by the radio). This implies that Cas A's magnetic field is continuously being amplified on small scales, as would be expected in a turbulent plasma.; (2) SNRs are known to accelerate cosmic rays to GeV range energies, and they are generally assumed to produce the majority of Galactic cosmic rays with energies below 1,000 TeV (the "knee"). We investigate X-ray synchrotron radiation from SNR shells, which is produced by high energy ({dollar}sim{dollar}10-100 TeV) electrons interacting with their local magnetic field. Evidence suggests that the X-ray spectra of a few SNRs contain a significant synchrotron component--thus confirming that they do accelerate high energy cosmic rays. In most cases, however, current X-ray spectroscopy cannot distinguish thermal from non-thermal emission, so the X-ray continua may, or may not be, of synchrotron origin. Upper limits can be found, however, simply by assuming that synchrotron radiation is the primary source of X-ray continuum. Maximum electron energies can then be derived by interpolating between the X-ray and radio synchrotron spectra. We have found that the electron energy upper limit for 14 of the brightest shell-type SNRs ill the Milky Way is significantly below the "knee," and in all cases, except one, the maximum electron energy is below 100 TeV. This strongly suggests that SNRs may still be the most likely source of CRs up to the "knee," but no further. |
