Revealing the heavily obscured AGN population of High Redshift 3CRR
  Sources with Chandra X-ray Observations
  Chandra observations of a complete, flux-limited sample of 38 high-redshift
(1<z<2), low-frequency selected (and so unbiased in orientation) 3CRR radio
sources are reported. The sample includes 21 quasars (= broad line radio
galaxies) and 17 narrow line radio galaxies (NLRGs) with matched 178 MHz radio
luminosity (log L_R ~ 44-45). The quasars have high radio core-fraction, high
X-ray luminosities (log L_X ~ 45-46) and soft X-ray hardness ratios (HR ~ -0.5)
indicating low obscuration. The NLRGs have lower core-fraction, lower apparent
X-ray luminosities (log L_X ~ 43-45) and mostly hard X-ray hardness ratios
(HR>0) indicating obscuration (log N_H ~ 22-24 cm^-2). These properties and the
correlation between obscuration and radio core-fraction are consistent with
orientation-dependent obscuration as in Unification models. About half the
NLRGs have soft X-ray hardness ratios and/or high [OIII] emission line to X-ray
luminosity ratio suggesting obscuration by Compton thick (CT) material so that
scattered nuclear or extended X-ray emission dominates (as in NGC1068). The
ratios of unobscured to Compton-thin (10^{22}< N_H(int) < 1.5 x 10^{24} cm^-2)
to CT (N_H(int) > 1.5 x 10^{24} cm^-2) is 2.5:1.4:1 in this high luminosity,
radio-selected sample. The obscured fraction is 0.5, higher than is typically
reported for AGN at comparable luminosities from multi-wavelength surveys
(0.1-0.3). Assuming random nuclear orientation, the unobscured half-opening
angle of the disk/wind/torus structure is ~ 60deg and the obscuring material
covers 30deg of which ~ 12deg is Compton thick. The multi-wavelength properties
reveal that many NLRGs have intrinsic absorption 10-1000x higher than indicated
by their X-ray hardness ratios, and their true L_X values are ~10--100x larger
than the hardness-ratio absorption corrections would indicate.
