Source of Pressure in Bubbles?

Pressure measured in X-ray shells is an order of mag. higher than the equipartition pressure measured from the radio source.
Magnetic field may be larger than equipartition value?
Contribution from low-energy relativistic electrons?
Very hot, diffuse thermal gas?
Chandra spectral limits on temp. of thermal component are not very restrictive. Limit for A2052 from lack of Faraday depolarization is kT > 20 keV. May be able to observe very hot gas directly with XMM-Newton.

Pressure measured in X-ray shells is an order of mag. higher than the equipartition pressure measured from the radio source.