ChandraandXMM‐NewtonObservations of a Sample of Low‐Redshift FR I and FR II Radio Galaxy Nuclei

We present spectral results, from Chandra and XMM-Newton observations, of asample of 22 low-redshift (z < 0.1) radio galaxies, and consider whether thecore emission originates from the base of a relativistic jet, an accretionflow, or contains contributions from both. We find correlations between theunabsorbed X-ray, radio, and optical fluxes and luminosities of FRI-typeradio-galaxy cores, implying a common origin in the form of a jet. On the otherhand, we find that the X-ray spectra of FRII-type radio-galaxy cores isdominated by absorbed emission, with $N_{\rm H} > 10^{23}$ atoms cm$^{-2}$,that is likely to originate in an accretion flow. We discuss several modelswhich may account for the different nuclear properties of FRI- and FRII-typecores, and also demonstrate that both heavily obscured, accretion-related, andunobscured, jet-related components may be present in all radio-galaxy nuclei.Any absorbed, accretion-related, components in FRI-type galaxies have lowradiative efficiencies.Comment: 44 pages, 5 figures. Minor typographical issues and reference in Section 4.4 updated. Accepted for publication in Ap