Determining the covering factor of Compton-thick active galactic nuclei with NuSTAR

Abstract

The covering factor of Compton-thick obscuring material associated with the torus in active galactic nuclei (AGN) is at present best understood through the fraction of sources exhibiting Compton-thick absorption along the line of sight ($N_H>1.5\times 10^{24}$ cm${}^{-2}$) in the X-ray band, which reveals the average covering factor. Determining this Compton-thick fraction is difficult however, due to the extreme obscuration. With its spectral coverage at hard X-rays ($>$10 keV), NuSTAR is sensitive to the AGN covering factor since Compton scattering of X-rays off optically thick material dominates at these energies. We present a spectral analysis of 10 AGN observed with NuSTAR where the obscuring medium is optically thick to Compton scattering, so called Compton-thick (CT) AGN. We use the torus models of Brightman & Nandra which predict the X-ray spectrum from reprocessing in a torus and include the torus opening angle as a free parameter and aim to determine the covering factor of the Compton-thick gas in these sources individually. Across the sample we find mild to heavy Compton-thick columns, with $N_H$ measured from $10^{24}-10^{26}$ cm${}^{-2}$, and a wide range of covering factors, where individual measurements range from 0.2-0.9. We find that the covering factor, $f_c$, is a strongly decreasing function of the intrinsic 2-10 keV luminosity, $L_X$, where $f_c=(-0.41\pm 0.13)$log${}_{10}$($L_X$/erg s${}^{-1}$)$+18.31\pm 5.33$, across more than two orders of magnitude in $L_X$ (10${}^{41.5}-10^{44}$ erg s${}^{-1}$). The covering factors measured here agree well with the obscured fraction as a function of $L_X$ as determined by studies of local AGN with $L_X>10^{42.5}$ erg s${}^{-1}$.

Accepted for publication in ApJ

References in corpus (17)

• Absorption Properties and Evolution of Active Galactic Nuclei
• Swift BAT Survey of AGN
• On the origin of soft X-rays in obscured AGN: answers from high-resolution spectroscopy with XMM-Newton
• Measuring the Fraction of Obscured Quasars by the Infrared Luminosity of Unobscured Quasars
• The 2-79 keV X-ray Spectrum of the Circinus Galaxy with NuSTAR, XMM-Newton and Chandra: a Fully Compton-Thick AGN
• Study on X-ray Spectra of Obscured AGNs based on Monte Carlo simulation - an interpretation of observed wide-band spectra
• The NuSTAR View of Nearby Compton-thick AGN: The Cases of NGC 424, NGC 1320 and IC 2560
• XMM and Chandra measurements of the AGN intrinsic absorption: dependence on luminosity and redshift
• Compton thick active galactic nuclei in Chandra surveys
• The Broad-band X-ray Spectrum of IC 4329A from a Joint NuSTAR/Suzaku Observation
• The variable hard X-ray emission of NGC4945 as observed by NuSTAR
• NuSTAR unveils a Compton-thick Type 2 quasar in Mrk 34
• The accretion ratios in Seyfert 2 galaxies with and without hidden broad-line regions
• An X-ray spectral model for clumpy tori in active galactic nuclei
• Coronal Properties of the Seyfert 1.9 Galaxy MCG -05-23-016 Determined from Hard X-ray Spectroscopy with NuSTAR
• NuSTAR Reveals the Comptonizing Corona of the Broad-Line Radio Galaxy 3C 382
• A Deep 0.3-10 keV Spectrum of the H${}_2$O Maser Galaxy IC 2560

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