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New Spectral Model for Constraining Torus Covering Factors from Broadband X-Ray Spectra of Active Galactic Nuclei

Baloković, M. and Brightman, M. and Harrison, F. A. and Comastri, A. and Ricci, C. and Buchner, J. and Gandhi, P. and Farrah, D. and Stern, D. (2018) New Spectral Model for Constraining Torus Covering Factors from Broadband X-Ray Spectra of Active Galactic Nuclei. Astrophysical Journal, 854 (1). Art. No. 42. ISSN 1538-4357. doi:10.3847/1538-4357/aaa7eb.

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The basic unified model of active galactic nuclei (AGNs) invokes an anisotropic obscuring structure, usually referred to as a torus, to explain AGN obscuration as an angle-dependent effect. We present a new grid of X-ray spectral templates based on radiative transfer calculations in neutral gas in an approximately toroidal geometry, appropriate for CCD-resolution X-ray spectra (FWHM ≥ 130 eV). Fitting the templates to broadband X-ray spectra of AGNs provides constraints on two important geometrical parameters of the gas distribution around the supermassive black hole: the average column density and the covering factor. Compared to the currently available spectral templates, our model is more flexible, and capable of providing constraints on the main torus parameters in a wider range of AGNs. We demonstrate the application of this model using hard X-ray spectra from NuSTAR (3–79 keV) for four AGNs covering a variety of classifications: 3C 390.3, NGC 2110, IC 5063, and NGC 7582. This small set of examples was chosen to illustrate the range of possible torus configurations, from disk-like to sphere-like geometries with column densities below, as well as above, the Compton-thick threshold. This diversity of torus properties challenges the simple assumption of a standard geometrically and optically thick toroidal structure commonly invoked in the basic form of the unified model of AGNs. Finding broad consistency between our constraints and those from infrared modeling, we discuss how the approach from the X-ray band complements similar measurements of AGN structures at other wavelengths.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Baloković, M.0000-0003-0476-6647
Brightman, M.0000-0002-8147-2602
Harrison, F. A.0000-0003-2992-8024
Comastri, A.0000-0003-3451-9970
Ricci, C.0000-0001-5231-2645
Buchner, J.0000-0003-0426-6634
Gandhi, P.0000-0003-3105-2615
Farrah, D.0000-0003-1748-2010
Stern, D.0000-0003-2686-9241
Additional Information:© 2018 American Astronomical Society. Received 2017 April 22. Accepted 2018 January 13. Published 2018 February 9. The authors thank the anonymous referee for careful reading and constructive suggestions that improved the paper. The authors gratefully acknowledge financial support from NASA Headquarters under the NASA Earth and Space Science Fellowship Program, grant NNX14AQ07H (M.B.), the ASI/INAF grant I/037/12/0–011/13 (A.C.), the Caltech Kingsley visitor program (A.C.), FONDECYT 1141218 (C.R.), Basal-CATA PFB–06/2007 (C.R.), and the China-CONICYT fund (C.R.). This work made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. We thank the NuSTAR Operations, Software, and Calibration teams for support with the execution and analysis of these observations. Furthermore, this research made use of the following resources: the NASA/IPAC Extragalactic Database (NED), operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration; the High Energy Astrophysics Science Archive Research Center Online Service, provided by the NASA/Goddard Space Flight Center; NASA's Astrophysics Data System; matplotlib, a Python library for publication quality graphics (Hunter 2007). Facility: NuSTAR - The NuSTAR (Nuclear Spectroscopic Telescope Array) mission.
Group:NuSTAR, Astronomy Department
Funding AgencyGrant Number
NASA Earth and Space Science FellowshipNNX14AQ07H
Agenzia Spaziale Italiana (ASI)I/037/12/0–011/13
Caltech Kingsley visitor programUNSPECIFIED
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)1141218
Istituto Nazionale di Astrofisica (INAF)UNSPECIFIED
Subject Keywords:galaxies: individual (3C 390.3, NGC 2110, IC 5063, NGC 7582) ; methods: data analysis; techniques: spectroscopic; X-rays: galaxies
Issue or Number:1
Record Number:CaltechAUTHORS:20180212-071654657
Persistent URL:
Official Citation:M. Baloković et al 2018 ApJ 854 42
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:84774
Deposited By: Ruth Sustaita
Deposited On:13 Feb 2018 17:47
Last Modified:15 Nov 2021 20:22

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