the intercept obtained from the most recent [*XMM-Newton*]{}/EPIC and [*Chandra*]{}/HEG works, along with the original [*Ginga*]{} work of @Iwasawa:1993ys.

![image](torus.ps){width="9cm"}

![image](CF_L.ps){width="9cm"}

An intriguing possibility is that the X-ray Baldwin effect is related to the decrease of the covering factor of the torus with luminosity (e.g., [@Page:2004kx], [@Zhou:2005ys]), in the frame of the [*luminosity-dependent unification*]{} schemes. The equivalent width of the iron K$\alpha$ line is in fact expected to be proportional to the covering factor of the torus (e.g., [@Krolik:1994fk], [@Ikeda:2009nx]), so that a covering factor of the torus decreasing with the luminosity might in principle be able to explain the X-ray Baldwin effect. Luminosity-dependent unification models have been proposed to explain the decrease of the fraction of obscured objects ($f_{\mathrm{obs}}$) with the increase of the AGN output power. The first suggestion of the existence of a relation between $f_{\mathrm{obs}}$ and the luminosity came about 30 years ago [@Lawrence:1982ys]. Since then the idea that the covering factor of the obscuring material decreases with luminosity has been gaining observational evidence from radio (e.g., [@Grimes:2004kx]), infrared (e.g., [@Treister:2008uq], [@Mor:2009fk], [@Gandhi:2009uq]), optical (e.g., [@Simpson:2005uq]) and X-ray (e.g., [@Ueda:2003qf], [@Beckmann:2009fk], [@Ueda:2011fk]) studies of AGN. Although luminosity-dependent unification models have been suspected for long to play 