Relativistic reflection from accretion disks in the population of Active Galactic Nuclei at z=0.5–4

Abstract

We report the detection of relativistically broadened iron Kα emission in the X-ray spectra of AGN detected in the 4Ms CDF-S. Using the Bayesian X-ray analysis (BXA) package, we fit 199 hard band (2-7 keV) selected sources in the redshift range z=0.5-4 with three models: (i) an absorbed power-law, (ii) the first model plus a narrow reflection component, and (iii) the second model with an additional relativistic broadened reflection. The Bayesian evidence for the full sample of sources selects the model with the additional broad component as being 10 5 times more probable to describe the data better than the second model. For the two brightest sources in our sample, CID 190 (z=0.734) and CID 104 (z=0.543), BXA reveals the relativistic signatures in the individual spectra. We estimate the fraction of sources containing a broad component to be 54 +35 −37 % (107/199 sources). Considering that the low signal-to-noise ratio of some spectra prevents the detection of the broad iron Kα line, we infer an intrinsic fraction with broad emission of around two thirds. The detection of relativistic signatures in the X-ray spectra of these sources suggests that they are powered by a radiatively efficient accretion disk. Preliminary evidence is found that the spin of the black hole is high, with a maximally spinning Kerr BH model (a=1) providing a significantly better fit than a Schwarzschild model (a=0). Our analysis demonstrate the potential of X-ray spectroscopy to measure this key parameter in typical SMBH systems at the peak of BH growth.

Probabilistic Detection of Spectral Line Components

“…We use the popular MultiNest (Feroz & Hobson 2008;Feroz et al 2009) implementation of nested sampling through the PyMultiNest (Buchner et al 2014) Python inter-face. This has been widely used in the past to perform model selection for astrophysical spectra (e.g., Bernardi et al 2016;Feldmeier-Krause et al 2017;Lavie et al 2017;Baronchelli et al 2018). The likelihood function was sampled through a wrapper to pyspeckit, specifically designed to perform nested sampling of spectral cubes 1 .…”

Do stellar-mass and super-massive black holes have similar dining habits?

“…The spin is another largely unconstrained and still lively debated quantity for both AGNs and XRBs (e.g. for GX 339−4, Kolehmainen & Done 2010;Parker et al 2016;Ludlam et al 2015;García et al 2015), although flux-limited AGN samples are likely biased in being preferentially populated by high spin sources from several different lines of reasoning (Brenneman et al 2011;Vasudevan et al 2016;Baronchelli et al 2018;Reynolds 2019), including modelling the L disc −L cor itself (Arcodia et al 2019). Moreover, the effect of the spin on the corona luminosity is likely degenerate with its geometry and extent and a thorough treatment of these unknowns is beyond the scope of this paper.…”

Are Compton-thin AGNs Globally Compton Thin?

“…Low equivalent width values from Suzaku observations (tens of eV, Fukazawa et al 2011a) have also been interpreted as evidence of narrow lines originating in distant material (Ricci et al 2014). In contrast, when the primary X-ray continuum is scattered close to the SMBH, Doppler and general relativistic effects combined may give rise to a significantly broader line (FWHM tens of thousands km s −1 ), reported in at least ∼36% of AGNs (de la Calle Pérez et al 2010; see also, e.g., Porquet et al 2004;Jiménez-Bailón et al 2005;Guainazzi et al 2006;Nandra et al 2007;Brenneman & Reynolds 2009;Patrick et al 2012;Liu & Li 2015;Mantovani et al 2016;Baronchelli et al 2018). In this case, contributions to the line's width become increasingly stronger as the primary continuum is scattered closer, and up to, the innermost stable circular orbit (ISCO), where the accretion disk's inner edge is located.…”