On the role of the Γ-λEdd relation on the X-ray Baldwin effect in active galactic nuclei

Abstract

The X-ray Baldwin effect is the inverse correlation between the equivalent width (EW) of the narrowcomponent of the iron Kα line and the X-ray luminosity of active galactic nuclei (AGN). A similar trend has also been observed between Fe Kα EW and the Eddington ratio (λEdd). Using Chandra/High Energy Grating results of Shu et al. and bolometric corrections we study the relation between EW and λEdd , and find that log EW = (-0.13 ± 0.03) log λEdd + 1.47. We explore the role of the known positive correlation between the photon index of the primary X-ray continuum Γ and λEdd on the X-ray Baldwineffect.We simulate the iron α line emitted by populations of unabsorbed AGN considering threedifferent geometries of the reflecting material: toroidal, spherical-toroidal and slab. We find that the Γ-Edd correlation cannotaccount for the whole X-ray Baldwin effect, unless a strong dependence of Γ on Edd, such as the one recently found by Risaliti etal. and Jin et al., is assumed. No clear correlation is found between EW and Γ. We concludethat a good understanding of the slope of the Γ-λEdd relation is critical to assess whether the trend plays a leading or rather a marginal role in the X-ray Baldwin effect. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.