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We present results from Chandra and XMM-Newton spectroscopic observations ofthe nuclei of z<0.5 radio galaxies and quasars from the 3CRR catalog, andexamine in detail the dichotomy in the properties of low- and high-excitationradio galaxies. The X-ray spectra of low-excitation sources (those with weak orabsent optical emission lines) are dominated by unabsorbed emission from aparsec-scale jet, with no contribution from accretion-related emission. Thesesources show no evidence for an obscuring torus, and are likely to accrete in aradiatively inefficient manner. High-excitation sources (those with prominentoptical emission lines), on the other hand, show a significant contributionfrom a radiatively efficient accretion disk, which is heavily absorbed in theX-ray when they are oriented close to edge-on with respect to the observer.However, the low-excitation/high-excitation division does not correspond to theFRI/FRII division: thus the Fanaroff-Riley dichotomy remains a consequence ofthe interaction between the jet and the hot-gas environment through which itpropagates. Finally, we suggest that accretion of the hot phase of the IGM issufficient to power all low-excitation radio sources, while high-excitationsources require an additional contribution from cold gas that in turn forms thecold disk and torus. This model explains a number of properties of theradio-loud active galaxy population, and has important implications for AGNfeedback mechanisms.

X-Ray Nuclei in Radio Galaxies: Exploring the Roles of Hot and Cold Gas Accretion