DETECTION OF INVERSE-COMPTON X-RAYS FROM LOBES OF THE RADIO GALAXY FORNAX-A

Extended X-ray emission was detected with ASCA from the synchrotron double lobes of the radio galaxy Fornax A. This is thought to be the same emission as was detected with ROSAT. The excess X-rays exhibit very hard spectra, described by a power law of energy index 1.2 +/- 0.5. Since this index is consistent with the synchrotron. radio index of 0.9 +/- 0.2, the X-rays are thought to arise when the radio-emitting relativistic electrons make inverse-Compton scattering off the cosmic microwave photons. Comparison of the X-ray and radio fluxes yields the lobe magnetic field intensity of 2-4 mu G. The relativistic electrons in the lobes are inferred to have an energy density close to that of the magnetic fields.