Comparison of hard X-ray spectra of luminous radio galaxies and their radio-quiet counterparts

Abstract

We study the differences in X-ray properties of luminous radio galaxies and their radio-quiet counterparts. In order to avoid biases associated with the dependence of X-ray properties on the black hole mass and Eddington ratio, the radio-loud and radioquiet objects are selected to cover similar ranges of these parameters. Our studies are based on the X-ray data from the Swift/BAT catalogue. We confirm previous results that radio galaxies are on average X-ray-louder than radio-quiet AGNs, but find that their spectral slopes are very similar. This suggests that in radio-loud and radio-quiet AGNs the hard X-rays are produced in the same region and by the same mechanism. We argue that this region can be associated with the hot, geometrically thick, central portion of the accretion flow, where production of hard X-rays is likely to be dominated by Comptonization of the optical/UV radiation of the truncated 'cold' accretion disc by hot electrons. The larger X-ray luminosities in radio-loud AGNs may result from larger radiative efficiencies of the innermost portions of the accretion flows around faster rotating black holes.

BAT AGN spectroscopic survey - XV: the high frequency radio cores of ultra-hard X-ray selected AGN

“…The redshift and Herschel-resolution cuts removed all radio-loud quasars (including FR I and FR II sources) from our sample. This is unsurprising, as such objects are intrinsically rare and tend to be higher redshift; for example, Gupta et al (2018) found that 51/509 (10 per cent) of the overall BAT AGN sample are radio-loud. The large majority of our remaining sources are therefore radioquiet Seyferts.…”

The origin of X-ray emission in 3CRR sources: hints from mid-infrared Spitzer observations

“…Starting from the 3CRR catalog 1 , we firstly selected the objects with an available black hole mass estimation, thus the Eddington ratio, which is a key parameter to investigate X-ray properties, can be calculated (e.g., Brandt & Alexander 2015;Gupta et al 2018;Li 2019). The black hole masses in 84 out of the total 173 objects were measured, where all of them were taken from McLure et al (2006) or Buttiglione et al (2010).…”

“…This seems to indicate that the X-ray emission from jets is important in RLAGNs. However, Gupta et al (2018) recently compiled an excellent sample to investigate the differences of Xray properties between luminous radio galaxies and their radioquiet counterparts, where the black hole mass and Eddington ratio were well selected and the bolometric luminosity were calculated from mid-infrared emission observed by the Wide-field Infrared Survey Explorer (WISE) mission. They argue that the X-ray emission in radio-loud radio galaxies should also come from a disk-corona system because their distribution of the Xray slope is very similar with those of radio-quiet counterparts (see Gupta et al 2018 for details, see also Gupta et al 2020).…”

“…The reasons we adopted midinfrared instead of optical-UV emission are as follows. 1) We wanted to take advantage of the bolometric luminosity calculated from mid-infrared emission and compare that with the results of Gupta et al (2018). 2) The big blue bump is obscured in a fraction of reddened quasars (see, e.g., Shang et al 2011;Zhou & Gu 2020).…”

X-ray Properties of 3C 111: Separation of Primary Nuclear Emission and Jet Continuum

“…Moreover in the NuSTAR observations of AGN populations no links were found between high energy cut-off and Eddington ratio, or BH mass [26,27]. Recent analysis of samples of non-blazar RL and RQ AGN of Swift/BAT catalogue also revealed that the photon indices and high-energy exponential cut-offs of RL and RQ AGN cover the same range of values and do not show significant differences between their distributions [28]. This addresses the questions both about physical conditions causing the cut-off absence in RL AGN or low values of cut-off in RQ ones.…”