Hot corona properties of Swift/BAT-detected AGNs

Abstract

Using a sample of 208 broad-line active galactic nuclei (AGNs) from Swift/BAT AGN Spectroscopic Survey in ultra-hard X-ray band (14 − 195 keV), the hot corona properties are investigated, i.e. the fraction of gravitational energy dissipated in the hot corona and the hard X-ray photon index. The bolometric luminosity, L Bol , is calculated from host-corrected luminosity at 5100Å. Virial supermassive black hole masses (SMBH, M BH ) are calculated from the Hβ line width and the corresponding broad line region size-luminosity empirical relation at 5100Å. We find a strong anti-correlation between the fraction of energy released in corona (F X ≡ L 14−195keV /L Bol ) and the Eddington ratio (ε ≡ L Bol /L Edd ), F X ∝ ε −0.60±0.1 . It is found that this fraction also has a correlation with the SMBH mass, BH. Assuming that magnetic buoyancy and feild reconnection lead to the formation of a hot corona, our result favours the shear stress tensor being a proportion of the gas pressure. For our entire sample, it is found that the hard X-ray photon index Γ has a weak but significant correlation with the Eddington ratio, Γ = 2.17 + 0.21 log ε. However, this correlation is not robust because the relation is not statistically significant for its subsample of 32 RM AGNs with relatively reliable M BH or its subsample of 166 AGNs with singleepoch M BH . We do not find a statistically significant relation between the photon index and the Eddington ratio taking into account an additional dependence on F X . disk. Therefore, the fraction of FX ≡ LX/L Bol (LX and L Bol are the X-ray luminosity and the bolometric luminosity respectively) can be obtained if the magnetic stress and energy transportation are assumed (e.g. Merloni & Fabian 2002). This may give us a possible opportunity to test the working magnetic stress from hard X-ray observations. The relation between the fraction of energy dissipated in the corona FX and the Eddington ratio ε (ε ≡ L Bol /L Edd , L Edd is the Eddington luminosity) was investigated by some authors (e.g. Merloni & Fabian 2002;Wang et al. 2004;Yang et al. 2006). For a compiled sample of 56 AGNs from ASCA observation, Wang et al. (2004) found a relation between FX and ε as FX ∝ ε −0.64±0.09 , where the X-ray luminosity in 2 − 10 keV is used. Considering a larger sample of 98 AGNs, Yang et al. (2006) found FX ∝ ε −0.66 . These results supported the magnetic stress tensor being the form of t rφ ∝ Pgas, where Pgas is the gas pressure. In their compiled sample, they only have nine sources with ultra-hard X-ray observations of INTEGRAL and Swift, and for other sources the luminosity in 2 − 150 kev is extrapolated from the 2-10 keV luminosity with a fixed photon index. A sample of more AGNs with direct harder X-ray than 2-10 keV is needed for further investigation, such as Swift/BAT. Another relation between the X-ray photon index Γ and c 0000 The Authors

On the Observational Difference Between the Accretion Disk-Corona Connections among Super- and Sub-Eddington Accreting Active Galactic Nuclei

“…There is still no clear understanding of the physics behind this empirical disk-corona connection. Simple qualitative explanations usually involve how the accretion power dissipation formula or the coronal size/structure changes with accretion rate (e.g., Merloni 2003;Wang et al 2004;Yang et al 2007;Lusso & Risaliti 2017;Kubota & Done 2018;Wang et al 2019;Jiang et al 2019;Arcodia et al 2019; see more discussion in Section 4.2). Nevertheless, our finding here that super-Eddington accreting AGNs follow basically the same α OX -L 2500 Å (L 2 keV -L 2500 Å ) relation as that for typical AGNs suggests that super-Eddington accreting AGNs, regardless of their geometrically thick accretion disks and the potential photon-trapping effects, likely share the same relation when dissipating the accretion power between the accretion disk and corona as sub-Eddington accreting AGNs.…”

“…A fraction ( f X ) of the accretion power carried away by the magnetic buoyancy is released via magnetic reconnection, thereby heating the corona (e.g., Galeev et al 1979;Di Matteo 1998;Liu et al 2002;Uzdensky & Goodman 2008). Based on these descriptions and the basic theory of the standard accretion disk (Shakura & Sunyaev 1973), analytic models of the accretion disk-corona system (e.g., Merloni 2003;Wang et al 2004;Yang et al 2007;Cao 2009;Lusso & Risaliti 2017;Kubota & Done 2018;Wang et al 2019;Arcodia et al 2019;Cheng et al 2020) predict a smaller energy dissipation fraction f X for an accretion disk with a higher L Bol /L Edd , as the accretion disk becomes more radiation-pressure dominated and the MRI grows less rapidly. Besides, the radiation magneto-hydrodynamic (MHD) simulations by Jiang et al (2014Jiang et al ( , 2019) also suggest a weaker (smaller f X ) and more compact corona when the accretion rate increases.…”

X-Ray Observations of a [C ii]-bright, z = 6.59 Quasar/Companion System

“…One potential reason for this spectral shape is that PJ231−20 is undergoing a significant burst of accretion in connection with the ongoing merger. A number of works (e.g., Pounds et al 1995;Bian & Zhao 2003;Porquet et al 2004;Brightman et al 2013Brightman et al , 2016Trakhtenbrot et al 2017;Ricci et al 2018;Wang et al 2019a) have identified a trend between Γ and λ Edd , where λ Edd = L bol /L Edd , such that larger values of Γ trend with increasing Eddington ratios. PJ231−20 is accreting at an Eddington ratio of λ Edd = 0.48 +0.11 −0.39 (Mazzucchelli et al 2017), although we note that the black hole mass -and thus the Eddington ratio -were derived using a relation with a 0.55 dex scatter on its zero point (Vestergaard & Peterson 2006), and thus Eddington or even super-Eddington accretion is not incompatible with previous data.…”

Magnetic-reconnection-heated corona in active galactic nuclei: refined disc-corona model and application to broad-band radiation

“…Furthermore, it has recently been suggested that the primary X-ray spectral slopes of AGNs depend on the Eddington ratio λ Edd (e.g. Brightman et al 2013;Trakhtenbrot et al 2017;Wang et al 2019). Specifically, AGNs showing flat spectra Γ ≤ 2 have generally lower Eddington ratios λ Edd ≤ 0.1, and the spectra steepen with the increase of λ Edd .…”