We report XMM-Newton observations of three FR II radio galaxies at redshifts between 0.85 and 1.34 , which show extended diffuse X-ray emission within the radio lobes , likely due to inverse-Compton up-scattering of the cosmic microwave background .
Under this assumption , through spectrum-fitting together with archival VLA radio observations , we derive an independent estimate of the magnetic field in the radio lobes of 3C 469.1 and compare it with the equipartition value .
We find concordance between these two estimates as long as the turnover in the energy distribution of the particles occurs at a Lorentz factor in excess of \sim 250 .
We determine the total energy in relativistic particles in the radio emitting lobes of all three sources to range between 3 - 8 \times 10 ^ { 59 } erg .
The nuclei of these X-ray sources are heavily-absorbed powerful AGN .