  We investigate the non-thermal X-ray emission from Cas A. For the hard X-ray
continuum we test the model proposed by Laming, which invokes bremsstrahlung
from electrons accelerated by lower hybrid plasma waves. The justification for
this model comes from our determination of a lower limit to the average
magnetic field of B > 0.5 mG, which suggest that most of the electron
populations are too much affected by synchrotron losses to produce X-ray
synchrotron emission. An exception is the X-ray emission from the rim
surrounding Cas A, seen in Chandra continuum images. The width of this rim of
1.5" to 4", can be used to infer the magnetic field near the shock front, for
which we estimate B = 0.08 - 0.16 mG, and electron energies of about 57 - 40
TeV. This is lower than the average magnetic field, but higher than what may be
expected from shocked interstellar medium, suggesting a high pre-shock magnetic
field, or rapid, post shock, field amplification. Combining the two magnetic
field measurements we have constructed a simple two zone model. Most of the
radio emission comes from inside Cas A, where the magnetic field is strong,
whereas the inverse Compton emission comes from near the shock front. Only for
our lower limit on the magnetic field strength near the shock front is it
possible to explain the recent detection of TeV emission by HEGRA with inverse
Compton, for which, in addition, we have to assume a rather high far infrared
photon density that should be twice as high as our best estimate of roughly 70
cm^{-3}. Pion decay is therefore likely to be the dominant emission from Cas A
at TeV energies.
