Beyond Simple AGN Unification with Chandra-observed 3CRR Sources
  Low-frequency radio selection finds radio-bright galaxies regardless of the
amount of obscuration by gas and dust. We report \chandra\ observations of a
complete 178~MHz-selected, and so orientation unbiased, sample of 44 $0.5<z<1$
3CRR sources. The sample is comprised of quasars and narrow-line radio galaxies
(NLRGs) with similar radio luminosities, and the radio structure serves as both
an age and an orientation indicator. Consistent with Unification, intrinsic
obscuration (measured by \nh, X-ray hardness ratio, and X-ray luminosity)
generally increases with inclination. However, the sample includes a population
not seen in high-$z$ 3CRR sources: NLRGs viewed at intermediate inclination
angles with \nh~$<10^{22}$~cm$^{-2}$. Multiwavelength analysis suggests these
objects have lower $L/L_{\rm Edd}$ than typical NLRGs at similar orientation.
Thus both orientation and $L/L_{\rm Edd}$ are important, and a
"radiation-regulated Unification" provides a better explanation of the sample's
observed properties. In comparison with the 3CRR sample at $1<z<2$, our
lower-redshift sample shows a higher fraction of Compton-thin NLRGs (45\% vs.\
29\%) but similar Compton-thick fraction (20\%), implying a larger covering
factor of Compton-thin material at intermediate viewing angles and so a more
"puffed-up" torus atmosphere. We posit that this is due to a range of $L/L_{\rm
Edd}$ extending to lower values in this sample. In contrast, at high redshifts
the narrower range and high $L/L_{\rm Edd}$ values allowed orientation (and so
simple Unification) to dominate the sample's observed properties.
