We present a uniform and systematic analysis of the 0.6–10 keV X-ray spectra of radio-loud active galactic nuclei ( AGN ) observed by ASCA .
The sample , which is not statistically complete , includes 10 Broad Line Radio Galaxies ( BLRGs ) , 5 radio-loud Quasars ( QSRs ) , 9 Narrow Line Radio Galaxies ( NLRGs ) , and 10 Radio Galaxies ( RGs ) of mixed FR I and FR II types .
For several sources the ASCA data are presented here for the first time .
The exposure times of the observations and the fluxes of the objects vary over a wide range ; as a result , so does the signal-to-noise ratio of the individual X-ray spectra .
At soft X-rays , about 50 % of NLRGs and 100 % of RGs exhibit a thermal plasma emission component , with a bimodal distribution of temperatures and luminosities .
This indicates that the emission arises in hot gas either in a surrounding cluster or loose group or in a hot corona , consistent with previous ROSAT and optical results .
At energies above 2 keV , a hard power-law component ( photon index , \Gamma \sim 1.7 - 1.8 ) is detected in 90 % of cases .
The power-law photon indices and luminosities in BLRGs , QSRs , and NLRGs are similar .
This is consistent with simple orientation-based unification schemes for lobe-dominated radio-loud sources in which BLRGs , QSRs , and NLRGs harbor the same type of central engine .
Moreover , excess cold absorption in the range 10 ^ { 21 } – 10 ^ { 24 } cm ^ { -2 } is detected in most ( but not all ) NLRGs , consistent with absorption by an obscuring torus , as postulated by unification scenarios .
The ASCA data provide initial evidence that the immediate gaseous environment of the X-ray source of BLRGs may be different than in Seyfert 1s : absorption edges of ionized oxygen , common in the latter , are detected in only one BLRG .
Instead we detect large columns of cold gas in a fraction ( \sim 44–60 % ) of BLRGs and QSRs , comparable to the columns detected in NLRGs , which is puzzling .
This difference hints at different physical and/or geometrical properties of the medium around the X-ray source in radio-loud AGN compared to their radio-quiet counterparts , that can be explored further with future X-ray observations .
For the full sample , the nuclear X-ray luminosity is correlated with the luminosity of the [ O iii ] emission line , the FIR emission at 12 \mu m , and the lobe radio power at 5 GHz .
The Fe K \alpha line is detected in 50 % of BLRGs and in one QSR , with a large range of intrinsic widths and equivalent widths .
In the handful of NLRGs where it is detected , the line is generally unresolved .
Comparing the average power-law photon indices of the various classes of radio-loud AGN to their radio-quiet counterparts from the literature , we find only a weak indication that the ASCA 2–10 keV spectra of BLRGs are flatter than those of Seyfert 1s of comparable X-ray luminosity .
This result is at odds with evidence from samples studied by other authors suggesting that radio-loud AGN have flatter spectra than radio-quiet ones .
Rather , it supports the idea that a beamed synchrotron self-Compton component related to the radio source ( jet ) is responsible for the flatter slopes in those radio-loud AGN .
We argue that because of the way those samples were constructed , beamed X-ray emission from the radio jets probably contributed to the observed X-ray spectra .

The sample studied here includes 6 Weak Line Radio Galaxies ( WLRGs ) , powerful radio galaxies characterized by [ O iii ] \lambda \lambda 4569 , 5007 lines of unusually low luminosity and by unusually high [ O ii ] / [ O iii ] line ratios .
The ASCA spectra of WLRGs can be generally decomposed into a soft thermal component with kT \sim 1 keV , plus a hard component , described either by a flat ( \langle \Gamma \rangle = 1.5 ) absorbed power law , or a very hot ( kT \sim 100 keV ) thermal bremmstrahlung model .
Their intrinsic luminosities are in the range L _ { 2 - 10 ~ { } keV } \sim 10 ^ { 40 } – 10 ^ { 42 } erg s ^ { -1 } , two orders of magnitude lower than in other sources in our sample .
If the hard X-ray emission is attributed to a low-luminosity AGN , an interesting possibility is that WLRGs represent an extreme population of radio galaxies in which the central black hole is accreting at a rate well below the Eddington rate .