Susanna Bisogni – INAF-IASF Milano
15 giugno 2022

Abstract

The relation between X-rays and UV luminosities in quasars, holding for several decades in both bands and over a wide redshift range, suggests that the physical mechanism regulating the energy transfer from the accretion disc to the hot corona must be universal. For the first time, we used X-ray spectroscopic data from the Chandra Source Catalog 2.0 for a sample of >2000 SDSS DR14 quasars, finding a smaller intrinsic dispersion in the Lx-Luv relation at high redshift (delta < 0.2 dex) with respect to studies using photometric data from catalogs and confirming its non-evolution up to z~4.5. If used to delve into the physics of accretion, however, the Lx-Luv relation can be also used to identify the “outsiders”, sources showing a different state of the accretion disc/hot corona system with respect to the average population. In this context, a sample of z~3 quasars with pointed XMM observations revealed the presence of a sub-population of X-ray-weak quasars ascribable to a radiatively inefficient state of the corona and whose optical properties hint to the presence of a powerful accretion disc wind. The combination of the statistics and the spectroscopic information available in the CSC2.0/SDSS sample paves the way for a deeper investigation of the central engine in AGN.”