Departament d'Astronomia i Astrofísica
Universitat de València

    Unification scenarios of Active Galactic Nuclei: an X-ray view

Claudio Ricci

ISDC - Science data center for Astrophysics, University of Geneva, Switzerland

Seminari del departament d'Astronomia i Astrofísica

Dimecres 23 maig 2012



Active Galactic Nuclei (AGN) are the most luminous persistent sources of radiation in the Universe. The unified model of AGN foresees that different types of AGN are intrinsically the same object, and that observational differences are solely due to different inclination angles with respect to an obscuring toroidal structure. However, recent results have shown that the anisotropic absorber appear to be clumpy and to have covering factors inversely proportional to the luminosity. The hard X-rays (>10 keV) are a very suitable energy band for studying the unified model. Absorption does not play an important role at these energies, allowing to have a direct look at the central engine of the AGN. By analyzing the INTEGRAL IBIS/ISGRI average hard X-ray (17-250 keV) spectra of ~200 radio-quiet local AGN, we recently found that more obscured AGN have a larger reflection component than less obscured ones, which cannot be easily explained by the unified model, but might require an intrinsic difference in the covering factor of the torus between different types of AGN. In my talk, I will present several unification scenarios, and discuss their possible relation with the observed decrease of the equivalent width of the iron Kalpha line with the luminosity (i.e. the X-ray Baldwin effect).