Evidence for inverse Compton emission in the powerful radio galaxy 3C 219

Spectral analysis of ROSAT PSPC and ASCA archive data and a recent ROSAT HR I observation of the powerful FRII radio galaxy 3C 219 reveal an absorbed p oint-like source, coincident with the nucleus, and a non-thermal extended c omponent aligned with the radio structure. The pointlike source can be read ily interpreted as a hidden quasar in the nucleus, giving further support t o the unification scheme of FRII radio galaxies and radio loud quasars. The coincidence between the X-ray (0.1-10 keV) and radio spectral slopes sugge st that most of the emission associated with the extended component is due to the inverse Compton process in the radio lobes. The extended circumnucle ar emission can be understood as Compton scattering of the IR-optical radia tion emitted by the hidden quasar and surrounding dusty/molecular torus. Th is is the first observational evidence supporting the existence of this eff ect, which also probes the relativistic electron spectrum at energies much lower than those involved in the synchrotron radio emission. The observed X -ray flux can be matched by assuming that the energy density of the relativ istic particles exceed the equipartition value by about a factor of 10. At larger distances from the nucleus (greater than or equal to 70 kpc) the inv erse Compton scattering with the cosmic microwave background photons become s more important and may explain the observed X-ray features if positive fl uctuations in the column densities of relativistic electrons are present. A lternatively, one cannot exclude with the present data a thermal contributi on by hot clumpy gas surrounding the radio lobes.