A2163 was observed by the RXTE satellite for \sim 530 ks during a 6 month period starting in August 2004 .
The cluster primary emission is from very hot intracluster gas with kT \sim 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 \sim 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 \sim 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 \sim 0.4 \pm 0.2 \mu G .