An overview is given of multiwavelength observations of young supernova
remnants, with a focus on the observational signatures of efficient cosmic ray
acceleration. Some of the effects that may be attributed to efficient cosmic
ray acceleration are the radial magnetic fields in young supernova remnants,
magnetic field amplification as determined with X-ray imaging spectroscopy,
evidence for large post-shock compression factors, and low plasma temperatures,
as measured with high resolution optical/UV/X-ray spectroscopy. Special
emphasis is given to spectroscopy of post-shock plasma's, which offers an
opportunity to directly measure the post-shock temperature. In the presence of
efficient cosmic ray acceleration the post-shock temperatures are expected to
be lower than according to standard equations for a strong shock. For a number
of supernova remnants this seems indeed to be the case.Comment: Invited review, to appear in the proceedings of "4th Heidelberg
International Symposium on High Energy Gamma-Ray Astronomy 2008
