  Lower limits to the intracluster magnetic field are derived from modeling
broad band X-ray spectra of 6 galaxy clusters with radio halos (A401, A754,
A1367, Coma (A1656), A2256, and A2319). The 0.7 - 10 keV spectra for all
clusters were obtained with the Advanced Satellite for Cosmology and
Astrophysics (ASCA) Gas Imaging Spectrometer (GIS). For A401, A754, A1367, and
A1656, data from the HEAO1-A2 High Energy Detector (HED) (2-60 keV) was
included in a joint fit to further constrain the allowed non-thermal component.
Upperlimits to the non-thermal X-ray emission are a factor of approximately 10
improvement over previous values. Lower limits to the average magnetic field
derived from these upperlimits and the radio spectral parameters range from
0.08 - 0.30 microGauss. A seed intracluster field amplified by turbulence from
galaxy motion through the intracluster medium should have an average value in
the range of 0.1-0.2 (Goldman & Rephaeli, 1991; De Young, 1992), thus the lack
of any detections makes it unlikely that field amplification is due to galaxy
wakes. In addition, all of these clusters have an asymmetric surface brightness
distribution while several also have X-ray spectroscopic evidence of a merger.
We suggest that cluster mergers rather than galaxy wakes are the source of the
magnetic field amplification.
