An X-ray spectral model for Compton-thick toroidal reprocessors
By K. Murphy, T. Yaqoob. 2009
387 citations recorded by the source corpus.
The central engines of both type 1 and type 2 active galactic nuclei are thought to harbour a toroidal structure that absorbs and reprocesses high-energy photons from the central X-ray source. Unique features in the reprocessed spectra can provide powerful physical constraints on the geometry, column density, element abundances and orientation of the circumnuclear matter. If the reprocessor is Compton-thick, the calculation of emission-line and continuum spectra that are suitable for direct fitting to X-ray data is challenging because the reprocessed emission depends on the spectral shape of the incident continuum, which may not be directly observable. We present new Monte Carlo calculations of Green's functions for a toroidal reprocessor that provide significant improvements over currently available models. The Green's function approach enables the construction of X-ray spectral fitting models that allow arbitrary incident spectra as part of the fitting process. The calculations are fully relativistic and have been performed for column densities that cover the Compton-thin to Compton-thick regime, for incident photon energies up to 500 keV. The Green's function library can easily be extended cumulatively to provide models that are valid for higher input energies and a wider range of element abundances and opening angles of the torus. The reprocessed continuum and fluorescent line emission due to Fe Kα, Fe Kβ and Ni Kα are treated self-consistently, eliminating the need for ad hoc modelling that is currently common practice. We find that the spectral shape of the Compton-thick reflection spectrum in both the soft and hard X-ray bands in our toroidal geometry is different compared with that obtained from disc models. A key result of our study is that a Compton-thick toroidal structure that subtends the same solid angle at the X-ray source as a disc can produce a reflection spectrum that is ∼6 times weaker than that from a disc. This highlights the widespread and erroneous interpretation of the so-called ‘reflection-fraction’ as a solid angle, obtained from fitting disc-reflection models to Compton-thick sources without regard for proper consideration of geometry.
Subfields: Astronomy and Astrophysics, Radiation
View Paper: https://www.semanticscholar.org/paper/987ece7675c1800179c023814fd957447c8f4b3a
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Citations in the corpus
- BAT AGN Spectroscopic Survey. V. X-Ray Properties of the Swift/BAT 70-month AGN Catalog (2017, methodology): “The two main features produced by reprocessing of X-ray radiation in neutral material are the iron Kα line at 6.4keV and a broad Compton “hump” peaking at ∼ 30keV (e.g., Matt et al. 1991, Murphy & Yaqoob 2009).”
- X-ray spectral modelling of the AGN obscuring region in the CDFS: Bayesian model selection and catalogue (2014, background): “Multiple inter-dependent interactions of several elements can realistically only be done by X-ray radiative transfer simulations for a fixed geometry (see e.g. Nandra & George 1994; Murphy & Yaqoob 2009; Brightman & Nandra 2011).”
- The Suzaku View of Highly Ionized Outflows in AGN. 1; Statistical Detection and Global Absorber Properties (2012, background): “Naturally, owing to the important effect it can have on the observed X-ray spectrum there are numerous models available for modelling the reflection component (e.g. pexrav/pexriv, Magdziarz & Zdziarski 1995; pexmon, Nandra et al. 2007; reflionx, Ross & Fabian 2005; xillver,10 Garcı́a & Kallman 2010;”
- THE NUCLEAR SPECTROSCOPIC TELESCOPE ARRAY (NuSTAR) HIGH-ENERGY X-RAY MISSION (2013, background): “While this was sufficient to confirm their existence, physical constraints generally are remarkably poor, and the complex range of expected spectral features (Murphy & Yaqoob 2009) remain largely untested.”
- An XMM–Newton spectral survey of 12 μm selected galaxies – I. X-ray data (2010, background): “This was shown by Murphy & Yaqoob (2009) who modelled reflection from a toroidal distribution of matter, finding that the reflection fraction can be underestimated in this way by a factor of ∼ 6.”
- New Spectral Model for Constraining Torus Covering Factors from Broadband X-Ray Spectra of Active Galactic Nuclei (2018, methodology): “For both models, the average torus column density is related to the equatorial column density (which is a fitting parameter) via a factor that depends on geometry: π/4 for MYtorus (calculated exactly; Murphy & Yaqoob 2009) and 0.66 for ctorus (estimated; Liu & Li 2014).”
- THREE-YEAR SWIFT–BAT SURVEY OF ACTIVE GALACTIC NUCLEI: RECONCILING THEORY AND OBSERVATIONS? (2010, methodology): “…case, we adopted an improved version of the model of Yaqoob (1997) which fully treats relativistic Compton scattering, i.e., the MYTorus model by Murphy & Yaqoob (2009) and Yaqoob et al. (2010).7 This model provides tables for the attenuation of the continuum emission (transmitted through the…”
- Growing supermassive black holes in the late stages of galaxy mergers are heavily obscured (2017, background): “…and reproduces the main features arising from the reprocessing of the primary X-ray radiation from neutral material (e.g., Matt et al. 1991; Murphy & Yaqoob 2009): a narrow FeKα line at 6.4 keV (e.g., Shu et al. 2010; Ricci et al. 2014a,b) and the Compton hump at ∼ 20 − 30 keV (e.g., Koss…”