ASCA measurements of nonthermal pressures in the radio lobes

A summary is presented of ASCA (Tanaka et al. 1994) results on inverse-Comptonized X-rays from lobes of radio galaxies, which are emitted when relativistic electrons constructing synchrotron radio lobes boost up the cosmic microwave background photons to the X-ray and gamma-ray energy. By comparing the two radiation fluxes, we derived the energy distribution between magnetic fields and the relativistic electrons, assuming the same relativistic electrons in the lobes produce the emissions. This method is essentially free from the energy equipartition assumption. A study on spatial distributions of the field and particle energy densities is also presented. Based on the results presented in this paper, we suggest particle domination in the lobes and at the formation of the lobe.