  It is pointed out that copius X-rays from the lobes of FRII radio galaxies
are expected as a natural consequence of the unification linking FRIIs and
radio-loud quasars. The detection of extended X-ray emission from 3C 219,
likely due to Inverse Compton scattering of the IR photons from a hidden quasar
with the relativistic electrons in the lobes, provides the first observational
evidence supporting this conjecture. The X-ray fluxes detected in the
directions of other five pwerful FRIIs with large redshifts may be similarly
accounted for (an alternative to a thermal origin from hot intracluster gas).
Much less energetic electrons than those producing the synchrotron radio
emission are involved in the process. Then the equipartition conditions imply
stronger fields, and significantly stronger internal pressures of the relativic
plasmas, than those derived with conventional equipartition equations. The
importance of this effect in the pressure balance with the confining
intergalactic gas is pointed out.
