Letter to the Editor
On the Iwasawa-Taniguchi effect of radio-quiet AGN
Dipartimento di Fisica, Università degli Studi Roma Tre, via della Vasca Navale 84, 00146 Roma, Italy e-mail: firstname.lastname@example.org
2 XMM-Newton Science Operations Center, European Space Astronomy Center, ESA, Apartado 50727, 28080 Madrid, Spain
Accepted: 15 March 2007
Aims.The existence of an anti-correlation between the Equivalent Width (EW) of the neutral narrow core of the iron Kα 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 = (1.73±0.03) + (-0.17±0.03) ), where EWFe is the EW of the neutral iron Kα line in eV andLX,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
© ESO, 2007