The role of the Gamma-Eddington ratio relation on the X-ray Baldwin
  effect in Active Galactic Nuclei
  The X-ray Baldwin effect is the inverse correlation between the equivalent
width (EW) of the narrow component of the iron Kalpha line and the X-ray
luminosity of active galactic nuclei (AGN). A similar trend has also been
observed between Fe Kalpha EW and the Eddington ratio (lambda_Edd). Using
Chandra/HEG results of Shu et al. (2010) and bolometric corrections we study
the relation between EW and the lambda_Edd, and find that log EW =
(-0.13+/-0.03)log(lambda_Edd) + 1.47. We explore the role of the known positive
correlation between the photon index of the primary X-ray continuum (Gamma) and
lambda_Edd on the X-ray Baldwin effect. We simulate the iron Kalpha line
emitted by populations of unabsorbed AGN considering 3 different geometries of
the reflecting material: toroidal, spherical-toroidal and slab. We find that
the Gamma-lambda_Edd correlation cannot account for the whole X-ray Baldwin
effect, unless a strong dependence of Gamma on lambda_Edd, such as the one
recently found by Risaliti et al. (2009) and Jin et al. (2012), is assumed. No
clear correlation is found between EW and Gamma. We conclude that a good
understanding of the slope of the Gamma-lambda_Edd relation is critical to
assess whether the trend plays a leading or rather a marginal role in the X-ray
Baldwin effect.
