A2163 was observed by the RXTE satellite for ~530 ks during a 6 month period, starting in 2004 August. 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 data sets) is obtained with a power-law secondary spectral component. The deduced parameters of the nonthermal (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 μG.
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Rephaeli et al. (2006) studied this question.
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