ASCA measurements of field-particle energy distribution in radio lobes Original Research Article

The ASCA detections of inverse-Compton (IC) X-rays from lobes of radio galaxies are reported. Significant IC X-rays are observed from radio lobes of Fornax A (Kaneda et al. 1995; Feigelson et al. 1995), Centaurus B (PKS 1343-601) and NGC 612. The energy density and magnetic field intensity in the lobes are sorted out by comparing the IC X-ray flux with the synchrotron radio flux. The results from Centaurus B strongly suggest particle domination in the lobes; meanwhile, X-ray and radio image analysis shows an outward increase in the magnetic energy density. The X-ray image and spectrum observed from NGC 612 reveal a heavily absorbed low luminosity core (nucleus) emission, together with an extended emission associated with the lobes. The extended source luminosity is rather close to the expected value assuming the equipartition state, although the possibility of particle dominant lobes cannot be excluded.