A growth-rate indicator for Compton-thick active galactic nuclei

Abstract

Due to their heavily obscured central engines, the growth rate of Compton-thick (CT) active galactic nuclei (AGN) is difficult to measure. A statistically significant correlation between the Eddington ratio, λ${}_{Edd}$, and the X-ray power-law index, Γ, observed in unobscured AGN offers an estimate of their growth rate from X-ray spectroscopy (albeit with large scatter). However, since X-rays undergo reprocessing by Compton scattering and photoelectric absorption when the line-of-sight to the central engine is heavily obscured, the recovery of the intrinsic Γ is challenging. Here we study a sample of local, predominantly Compton-thick megamaser AGN, where the black hole mass, and thus Eddington luminosity, are well known. We compile results on X-ray spectral fitting of these sources with sensitive high-energy (E> 10 keV) NuSTAR data, where X-ray torus models which take into account the reprocessing effects have been used to recover the intrinsic Γ values and X-ray luminosities, L${}_X$. With a simple bolometric correction to L${}_X$ to calculate λ${}_{Edd}$, we find a statistically significant correlation between Γ and λ${}_{Edd}$ (p = 0.007). A linear fit to the data yields Γ = (0.41$\pm$0.18)log${}_{10}$λ${}_{Edd}$+(2.38$\pm$ 0.20), which is statistically consistent with results for unobscured AGN. This result implies that torus modeling successfully recovers the intrinsic AGN parameters. Since the megamasers have low-mass black holes (M${}_{BH}\approx 10^6-10^7$ M${}_{sol}$) and are highly inclined, our results extend the Γ-λ${}_{Edd}$ relationship to lower masses and argue against strong orientation effects in the corona, in support of AGN unification. Finally this result supports the use of Γ as a growth-rate indicator for accreting black holes, even for Compton-thick AGN.

Accepted for publication in ApJ

References in corpus (19)

• The Cosmic Evolution Survey (COSMOS) -- Overview
• Some Aspects of Measurement Error in Linear Regression of Astronomical Data
• An Observational Determination of the Bolometric Quasar Luminosity Function
• Piecing Together the X-ray Background: Bolometric Corrections for Active Galactic Nuclei
• eROSITA Science Book: Mapping the Structure of the Energetic Universe
• The Hard X-ray Spectrum as a Probe for Black-Hole Growth in Radio-Quiet Active Galactic Nuclei
• The Hard X-ray Spectral Slope as an Accretion-Rate Indicator in Radio-Quiet Active Galactic Nuclei
• Correlation between the photon index and X-ray luminosity of black hole X-ray binaries and active galactic nuclei: observations and interpretation
• The 2-79 keV X-ray Spectrum of the Circinus Galaxy with NuSTAR, XMM-Newton and Chandra: a Fully Compton-Thick AGN
• The XMM-Newton long look of NGC 1365: uncovering of the obscured X-ray source
• The NuSTAR View of Nearby Compton-thick AGN: The Cases of NGC 424, NGC 1320 and IC 2560
• The variable hard X-ray emission of NGC4945 as observed by NuSTAR
• NuSTAR unveils a Compton-thick Type 2 quasar in Mrk 34
• Determining the covering factor of Compton-thick active galactic nuclei with NuSTAR
• Inclination-dependent spectral and timing properties in transient black hole X-ray binaries
• Broadband Observations of the Compton-thick Nucleus of NGC 3393
• The Parsec-scale Accretion Disk in NGC 3393
• An X-ray spectral model for clumpy tori in active galactic nuclei
• Anisotropic radiation from accretion disc-coronae in active galactic nuclei

Cited by in corpus (11)

• High-redshift AGN in the Chandra Deep Fields: the obscured fraction and space density of the sub-$L_{\ast }$ population
• Galaxy gas as obscurer: II. Separating the galaxy-scale and nuclear obscurers of Active Galactic Nuclei
• NuSTAR observations of WISE J1036+0449, a Galaxy at z$\sim 1$ obscured by hot dust
• Heavy X-ray obscuration in the most-luminous galaxies discovered by WISE
• X-ray bolometric corrections for Compton-thick active galactic nuclei
• Was 49b: An Overmassive AGN in a Merging Dwarf Galaxy?
• IC 3639 - A new bona fide Compton thick AGN unveiled by NuSTAR
• Evidence for Relativistic Disk Reflection in the Seyfert 1h Galaxy/ULIRG IRAS 05189-2524 Observed by NuSTAR and XMM-Newton
• Peering through the dust II: $XMM-Newton$ observations of two additional FIRST-2MASS red quasars
• Investigating the evolution of the dual AGN system ESO~509-IG066
• The NuSTAR View of the Seyfert 2 Galaxy NGC 4388