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C. Delzer, M. Henriksen (Univ. of North Dakota)
An 8.3 hour observation of the Abell 2256 galaxy cluster using the Rossi X-ray Timing Explorer (RXTE) proportional counter array (PCA) produced a high quality spectrum in the 2 - 30 keV range. Joint fitting with the 0.7 - 11 keV spectrum obtained with the Advanced Satellite for Astrophysics and Cosmology (ASCA) Gas Imaging spectrometer (GIS) gives an upperlimit of ~2.3\times10-7 photons cm-2 sec-1 keV-1 for non-thermal emission at 30 keV. This yields a lower limit to the mean magnetic field of 0.36\muG and an upperlimit of 1.8\times10-13 ergs cm-3 for the cosmic-ray electron energy density. The resulting lower limit to the central magnetic field is ~1 - 3 \muG. While a magnetic field of ~0.1 - 0.2 \muG can be created by galaxy wakes, a magnetic field of several \muG is usually associated with a cooling flow or, as in the case of the Coma cluster, a subcluster merger. However, for A2256, the evidence for a merger is weak and the main cluster shows no evidence of a cooling flow. Thus, there is presently no satisfactory hypothesis for the origin of an average cluster magnetic field as high as > 0.36 \muG in the A2256 cluster.