Abstract
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.
Highlights
The standard model for the nuclear regions of an active galaxy includes a supermassive black hole (SMBH) surrounded by an accretion disk (AD) and a corona producing strong, thermal optical–UV–soft-X-ray and non-thermal X-ray emission
This paper describes the 3CRR sample (Section 2), presents our analysis of new and existing Chandra and XMM-Newton data (Section 3), characterizes the X-ray properties and investigates their relation to radio and IR emission (Section 4), discusses the results in the context of unification models (Section 5), and summarizes the conclusions (Section 6)
In order to provide a uniform set of derived X-ray properties, all Chandra-observed sources were run through an automated spectral analysis process using the Levenberg–Marquardt optimization method in CIAO/Sherpa with the χ 2 statistic including the Gehrels variance function, which allows for a Poisson distribution for low-count sources
Summary
The standard model for the nuclear regions of an active galaxy (active galactic nucleus, AGN) includes a supermassive black hole (SMBH) surrounded by an accretion disk (AD) and a corona producing strong, thermal optical–UV–soft-X-ray and non-thermal X-ray emission. The AD and corona, possibly combined with a larger torus and/or wind (Elvis 2000; Konigl & Kartje 1994), provide obscuration which is anisotropic and strongly frequency dependent and results in complex, orientation-dependent selection effects for observations in most wavebands. This affects both source detection and classification. The orientation dependence of the observed spectral energy distributions (SEDs) of AGNs results in differing levels of bias against most obscured sources in traditional optical/ultraviolet/near-infrared/soft X-ray surveys. One caveat to an RL sample is that only ∼10% of AGNs are RL, and they may not accurately represent the majority AGN population, e.g., radio-emitting plasma may affect the opening angle of the torus (Falcke et al 1995), and generally the X-ray emission includes an extra extended component related to the radio core and jet
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