Astronomy & Astrophysics

Free access article

Issue		A&A Volume 467, Number 1, May III 2007
Page(s)		L19 - L22
Section		Letters
DOI		10.1051/0004-6361:20077331

A&A 467, L19-L22 (2007)
DOI: 10.1051/0004-6361:20077331

Letter

On the Iwasawa-Taniguchi effect of radio-quiet AGN

S. Bianchi^{1, 2}, M. Guainazzi², G. Matt¹, and N. Fonseca Bonilla²

¹ Dipartimento di Fisica, Università degli Studi Roma Tre, via della Vasca Navale 84, 00146 Roma, Italy
e-mail: bianchi@fis.uniroma3.it
² XMM-Newton Science Operations Center, European Space Astronomy Center, ESA, Apartado 50727, 28080 Madrid, Spain

(Received 19 February 2007 / Accepted 15 March 2007)

Abstract
Aims.The existence of an anti-correlation between the Equivalent Width (EW) of the neutral narrow core of the iron K $\alpha$ 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 at testing this claim on the largest catalogue of radio quiet AGN high-quality X-ray spectra ever published.
Methods.The final sample comprises 157 objects. We search for a relation of the iron line EW not only with the X-ray luminosity, but 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.
Results.A linear censored fit on the EW versus 2-10 keV luminosity is highly significant and yields $\log(EW_{\rm Fe})$ = (1.73 $\pm$ 0.03) + (-0.17 $\pm$ 0.03) $\log(L_{\rm X,44}$ ), where $EW_{\rm Fe}$ is the EW of the neutral iron K $\alpha$ line in eV and $L_{\rm X,44}$ is the 2-10 keV X-ray luminosity in units of 10⁴⁴ 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.

Key words: galaxies: active -- galaxies: Seyfert -- quasars: general -- X-rays: general

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