On the Iwasawa-Taniguchi effect of radio-quiet AGN

The existence of an anti-correlation between the Equivalent Width (EW) of the neutral narrow core of the iron Kalpha emission line and the 2-10 keV luminosity (the so-called `X-ray Baldwin' or `Iwasawa-Taniguchi' effect) has been debated in the last years. We aim to test this claim using the largest catalog of radio quiet AGN with high-quality X-ray spectra ever published. Our final sample comprises 157 objects. We search for a relation of the iron line EW with the X-ray luminosity, also with the Black Hole mass, the Eddington ratio and the cosmological distance. The data presented here were analyzed homogeneously, all spectra are from the same instrument and with high Signal-to-Noise Ratio. A linear censored fit of the EW versus 2-10 keV luminosity is highly significant and yields log(EW) = (1.73+/-0.03)+(-0.17+/-0.03) log(L_X), where EW is the EW of the neutral iron Kalpha line in eV and L_X is the 2-10 keV X-ray luminosity in units of 10(44) erg s(-1) . The anti-correlation with the Eddington ratio is also very significant, while no dependence of the iron EW on the BH mass is apparent.