  We performed a spectral analysis of some Chandra ACIS and RXTE PCA data for
the supernova remnant Cas A. A very large (1.1 Ms) ACIS data set is used to
identify regions dominated by synchrotron radiation. The best-fit spectral
models for these regions are combined to obtain a composite synchrotron model
for the entire remnant. The difference between this model and the observed PCA
flux is fitted with a nonthermal bremsstrahlung model. The results of this
analysis suggest that (1) the ratio of the nonthermal bremsstrahlung to
synchrotron radiation varies from about 2:1 to 4:1 in the 10-32 keV energy
band, (2) the electron spectrum is significantly steeper at 10-32 keV than it
is at 1 GeV, (3) about 5% of the electrons are nonthermal and (4) about 30% of
the energy in the electron distribution is in nonthermal electrons.
