The Hard X-Ray Spectral Slope as an Accretion Rate Indicator in Radio-quiet Active Galactic Nuclei
By O. Shemmer, W. N. Brandt, H. Netzer, R. Maiolino, S. Kaspi. 2006
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We present new XMM-Newton observations of two luminous and high accretion rate radio-quiet active galactic nuclei (AGNs) at z ~ 2. Together with archival X-ray and rest-frame optical spectra of three sources with similar properties, as well as 25 moderate-luminosity radio-quiet AGNs at z < 0.5, we investigate, for the first time, the dependence of the hard (≳2 keV) X-ray power-law photon index on the broad Hβ emission-line width and on the accretion rate across ~3 orders of magnitude in AGN luminosity. Provided that the accretion rates of the five luminous sources can be estimated by extrapolating the well-known relation between the broad-line region size and luminosity to high luminosities, we find that the photon indices of these sources, while consistent with those expected from their accretion rates, are significantly higher than expected from the widths of their Hβ lines. We argue that within the limits of our sample, the hard X-ray photon index depends primarily on the accretion rate.
Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics
View Paper: https://www.semanticscholar.org/paper/ff38498b08975deb645291746cc7a30003adb541
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Citations in the corpus
- The X-Ray Properties of the Most Luminous Quasars from the Sloan Digital Sky Survey (2007, methodology): “There is evidence, however, that the photon index (Γ) of the X-ray power-law spectrum increases asL/LEdd increases (e.g., Shemmer et al. 2006b) and that the X-ray-to-optical flux ratio (αox; Tananbaum et al. 1979) drops with increasing luminosity.”
- Some Aspects of Measurement Error in Linear Regression of Astronomical Data (2007, background): “Recent work has suggested a correlation between quasar X-ray spectral slope, αX , fν ∝ ν −αX , and quasar Eddington ratio, Lbol/LEdd (e.g., Porquet et al. 2004; Piconcelli et al. 2005; Shemmer et al. 2006).”
- A physical model of the broad-band continuum of AGN and its implications for the UV/X relation and optical variability (2018, background): “…by a decrease in Rcorona/Rg (where Rg = GM/c2) correlated with a increase in the hot Comptonisation power law spectra index as Lbol/LEdd increases (Jin et al. 2012a,b; Ezhikode et al. 2017; see also Shemmer et al. 2006, 2008 and Vasudevan & Fabian 2007, 2009 for the hard X-ray spectral index).”
- Piecing together the X-ray background : bolometric corrections for active galactic nuclei (2007, result): “The dependence of the X-ray photon index on Eddington ratio in AGN has been commented on by other authors including Shemmer et al. (2006), who find a correlation betwenΓ andLbol/LEdd.”
- A statistical relation between the X-ray spectral index and Eddington ratio of active galactic nuclei in deep surveys (2013, background): “Subsequently λEdd was shown to be strongly correlated with (Lu & Yu 1999; Wang, Watarai & Mineshige 2004; Shemmer et al. 2006).”
- Simultaneous X-ray/optical/UV snapshots of active galactic nuclei from XMM–Newton: spectral energy distributions for the reverberation mapped sample (2008, result): “The work of Shemmer et al. (2006) highlights a correlation between the hard Xray photon index Γ and λEdd for AGN, reinforced in their later work (Shemmer et al. 2008).”
- X-RAY SPECTRAL PROPERTIES OF THE BAT AGN SAMPLE (2008, background): “First, the 30 objects selected by Shemmer et al. (2006) are moderate to high luminosity RQQs.”