DOI:
10.1051/0004-6361/202141829
Authors:
Laurenti, M.;Piconcelli, E.;Zappacosta, L.;Tombesi, F.;Vignali, C.;Bianchi, S.;Marziani, P.;Vagnetti, F.;Bongiorno, A.;Bischetti, M.;Del Olmo, A.;Lanzuisi, G.;Luminari, A.;Middei, R.;Perri, M.;Ricci, C.;Vietri, G.
Journal:
Astronomy and Astrophysics
Abstract:
Improving our understanding of the nuclear properties of high-Eddington-ratio (λEdd) active galactic nuclei (AGN) is necessary since at this regime the radiation pressure is expected to affect the structure and efficiency of the accretion disc-corona system. This may cause departures from the typical nuclear properties of low-λEdd AGN, which have been largely studied so far. We present here the X-ray spectral analysis of 14 radio-quiet, λEdd ≥ 1 AGN at 0.4 ≤ z ≤ 0.75, observed with XMM-Newton. Optical/UV data from simultaneous Optical Monitor observations have also been considered. These quasars were selected to have relatively high values of black hole mass (MBH ~ 108-8.5 M⊙) and bolometric luminosity (Lbol ~ 1046 erg s-1) in order to complement previous studies of high- λEdd AGN at lower MBH and Lbol. We studied the relation between λEdd and other key X-ray spectral parameters, such as the photon index (Γ) of the power-law continuum, the X-ray bolometric correction (kbol,X), and the optical/UV-to-X-ray spectral index (αox). Our analysis reveals that, despite the homogeneous optical and supermassive black hole accretion properties, the X-ray properties of these high-λEdd AGN are quite heterogeneous. We indeed measured values of Γ between 1.3 and 2.5, at odds with the expectations based on previously reported Γ-λEdd relations, for which Γ ≥ 2 would be a ubiquitous hallmark of AGN with λEdd ~ 1. Interestingly, we found that ~30% of the sources are X-ray weak, with an X-ray emission about a factor of ~10-80 fainter than that of typical AGN at similar UV luminosities. The X-ray weakness seems to be intrinsic and not due to the presence of absorption along the line of sight to the nucleus. This result may indicate that high-λEdd AGN commonly undergo periods of intrinsic X-ray weakness. Furthermore, results from follow-up monitoring with Swift of one of these X-ray weak sources suggest that these periods can last for several years.
URL:
https://ui.adsabs.harvard.edu/#abs/2022A&A...657A..57L/abstract
Keywords:
Galaxies: active | Quasars: general | Quasars: supermassive black holes