Studying the relationship between X-ray emission and accretion in AGN using the XMM-Newton Bright Serendipitous Survey

• Published in: Monthly notices of the Royal Astronomical Society Vol. 433; no. 1; pp. 648 - 658
• Main Authors: Fanali, R., Caccianiga, A., Severgnini, P., Della Ceca, R., Marchese, E., Carrera, F. J., Corral, A., Mateos, S.
• Format: Journal Article
• Language: English
• Published: London Oxford University Press 21.07.2013
• Subjects: Accretion disks; Corona; Correlation analysis; Luminosity; Star & galaxy formation; X-ray astronomy; quasars: general; galaxies: nuclei; galaxies: active; X-rays: galaxies
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stt757

We study the link between the X-ray emission in radio-quiet active galactic nuclei (AGN) and the accretion rate on the central supermassive black hole using a statistically well-defined and representative sample of 71 type 1 AGN extracted from the XMM-Newton Bright Serendipitous Survey. We search and quantify the statistical correlations between some fundamental parameters that characterize the X-ray emission, i.e. the X-ray spectral slope, Γ, and the X-ray 'loudness', and the accretion rate, both absolute (Ṁ) and normalized to the Eddington luminosity (Eddington ratio, λ). We parametrize the X-ray loudness using three different quantities: the bolometric correction K bol, the two-point spectral index αOX and the disc/corona luminosity ratio. We find that the X-ray spectral index depends on the normalized accretion rate while the 'X-ray loudness' depends on both the normalized and the absolute accretion rate. The dependence on the Eddington ratio, in particular, is probably induced by the Γ - λ correlation. The two proxies usually adopted in the literature to quantify the X-ray loudness of an AGN, i.e. K bol and αOX, behave differently, with K bol being more sensitive to the Eddington ratio and αOX having a stronger dependence with the absolute accretion. The explanation of this result is likely related to the different sensitivity of the two parameters to the X-ray spectral index.