X-ray spectroscopic survey of highly-accreting AGN

Abstract

Improving our understanding of the nuclear properties of high-Eddington ratio (λ Edd ) 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-λ Edd AGN, which have been largely studied so far. We present here the X-ray spectral analysis of 14 radio-quiet, λ Edd 1 AGN at 0.4 ≤ z ≤ 0.75, observed with XMM-Newton. Optical/UV data from simultaneous Optical Monitor observations have been also considered. These quasars have been selected to have relatively high values of black hole mass (M BH ∼ 10 8−8.5 M ) and bolometric luminosity (L bol ∼ 10 46 erg s −1 ), in order to complement previous studies of high-λ Edd AGN at lower M BH and L bol . We studied the relation between λ Edd and other key X-ray spectral parameters, such as the photon index (Γ) of the power-law continuum, the X-ray bolometric correction k bol,X and the optical/UV-to-X-ray spectral index α ox . Our analysis reveals that, despite the homogeneous optical and SMBH accretion properties, the X-ray properties of these high-λ Edd AGN are quite heterogeneous. We indeed measured values of Γ comprised between 1.3 and 2.5, at odds with the expectations based on previously reported Γ − λ Edd relations, by which Γ ≥ 2 would be an ubiquitous hallmark of AGN with λ Edd ∼ 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-λ Edd AGN commonly undergo periods of intrinsic X-ray weakness. Furthermore, results from a follow-up monitoring with Swift of one of these X-ray weak sources suggest that these periods can last for several years.

Tell-Tale Spectral Signatures of MHD-driven Ultra-Fast Outflows in AGNs

“…As addressed earlier, the mass accretion rate (thus the wind density normalization parameterized by f D ) should in reality be physically coupled to the X-ray luminosity and perhaps α OX , for example, as suggested in the past studies (e.g. Steffen et al 2006;Shemmer et al 2008;Luo et al 2014;Laurenti et al 2021). For this reason, it is not our primary interest to compare the absolute line properties (i.e.…”

“…Γ, α OX , Eddington ratio and monochromatic UV luminosities (e.g. Steffen et al 2006;Shemmer et al 2008;Luo et al 2014;Laurenti et al 2021). Although these correlations are preferentially suggested in highly-accreting quasars, this may well be relevant for Seyfert 1s accreting at low Eddington rate.…”

“…magneto-centrifugal and magnetic pressure forces; e.g. Blandford & Payne 1982;Contopoulos & Lovelace 1994;Köngl & Kartje 1994;Ferreira 1997;Everett 2005;Fukumura et al 2010aFukumura et al ,b, 2015Fukumura et al , 2018Chakravorty et al 2016;Kraemer et al 2018;Jacquemin-Ide et al 2019, 2021.…”

Deep XMM-Newton Observations of an X-ray Weak, Broad Absorption Line Quasar at $z=6.5$

“…A very high accretion rate is also discussed as one possible reason for the intrinsic X-ray weakness of BAL quasars (e.g., Leighly et al 2007;Luo et al 2014). Laurenti et al (2021) recently report a high Xray weak fraction (∼ 30%) among high-Eddington ratio AGN. For J0439+1634, its NIR spectral fitting shows an Eddington ratio (L bol /L Edd ) of 0.6±0.1 (L bol = (4.6 ± 0.1) × 10 46 erg s −1 , M BH = (6.3 ± 0.2) × 10 8 M ), which is not high compared to the median value (i.e., 0.85; a mean of 1.08) for z ∼ 6.5 quasars (Yang et al 2021).…”