  A2163 was observed by the RXTE satellite for 530 ks during a 6 month period
starting in August 2004. The cluster primary emission is from very hot
intracluster gas with kT~15 keV, but this component does not by itself provide
the best fitting model. A secondary emission component is quite clearly needed,
and while this could also be thermal at a temperature significantly lower than
kT~15 keV, the best fit (to the combined PCA and HEXTE datasets) is obtained
with a power law secondary spectral component. The deduced parameters of the
non-thermal (NT) emission imply a significant fractional flux amounting to ~25%
of the integrated 3-50 keV emission. NT emission is expected given the intense
level of radio emission, most prominently from a large extended (`halo')
central region of the cluster. Interpreting the deduced NT emission as Compton
scattering of the radio-emitting relativistic electrons by the CMB, we estimate
the volume-averaged value of the magnetic field in the extended radio region to
be B=0.4+/-0.2 microG.
