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

Abstract

Spectral analysis of ROSAT PSPC and ASCA archive data and a recent ROSAT HRI observation of the powerful FRII radio galaxy 3C 219 reveal an absorbed point-like source, coincident with the nucleus, and a non-thermal extended component aligned with the radio structure. The point-like source can be readily interpreted as a hidden quasar in the nucleus, giving further support to the unification scheme of FRII radio galaxies and radio loud quasars. The coincidence between the X-ray (0.1-10 keV) and radio spectral index suggest that most of the emission associated with the extended component is due to the inverse Compton process in the radio lobes. The extended circumnuclear emission can be understood as Compton scattering of the IR-optical radiation emitted by the hidden quasar and surrounding dusty/molecular torus. This is the first observational evidence supporting the existence of this effect, 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 relativistic particles exceed the equipartition value by about a factor of 10. At larger distances from the nucleus ($\geq 70$kpc) the inverse Compton scattering with the cosmic microwave background photons becomes more important and may explain the observed X-ray features if positive fluctuations in the column densities of relativistic electrons are present. Alternatively, one cannot exclude with the present data a thermal contribution by hot clumpy gas surrounding the radio lobes.