Ctorus model

This is an X-ray spectral model for clumpy tori in active galactic nuclei, which is the output spectrum of a clumpy torus illuminated by the central active galactic nuclei. This model is comprehensively explained in Liu, Y., & Li, X. 2014, ApJ, 787, 52. See more applications in Liu, Y., & Li, X. 2015, MNRAS, 448, L53 and Liu, J., Liu, Y., Li, X., et al. 2016, MNRAS, 459, L100.

The incident X-ray spectrum from the central active galactic nuclei is a power law. The half-opening angle of the torus (the envelope of clouds) is fixed at 60 degrees. This model can be applied in 1.0 - 450 keV and includes three parts, i.e., transmitted component (Ctorus_T.fits), reflection component (Ctorus_R.fits), and fluorescent lines (Ctorus_L.fits).

The transmitted component is the power law absorbed by a given column density NH, which is the only parameter of this component. Since the scattering cross section is included, the absorption is more significant compared with wabs or phabs with the same value of nominal NH.

  • NH: the column density along our line of sight, in the units of 10^23 cm^-2, from 0.1 to 100
The reflection component is the collection of photons that have experienced the Compton and/or Rayleigh scattering with the torus.
  • N: the average number of clouds along the radial direction, from 2 to 10
  • NH: the total column density if N clouds are exactly aligned along the radial direction, in the units of 10^23 cm^-2, from 1 to 100.
  • Costheta: the cosine value of observing angle (the angle between our line of sight and the rotation axis of the torus), from 0.05 (edge-on) to 0.95 (face-on).
  • Gamma: the photon index of the incident power law, from 1.5 to 2.5
The parameters in the fluorescent lines are the same as those in the reflection component. The current model has included the Kalpha lines of Mg, Al, Si, S, Ar, Ca, Fe, and Ni, and the Kbeta lines of Ca, Fe, and Ni. The Compton shoulder is not included in the current version.

The basic usage of the Ctorus model is mtable{Ctorus_T.fits}*powerlaw + atable{Ctorus_R.fits} + atable{Ctorus_L.fits}

  • Due to the clumpy geometry, the value of NH in the Ctorus_T is not necessarily the same as that in other components. Please see the subtle difference of several column densities in section 3 of Liu & Li (2014).
  • The gamma and norm in Ctorus_T should be linked to the PhoIndex and norm in powerlaw, unless e.g. you think the incident spectrum from the active galactic nuclei is anisotropic (amplitude or shape).
  • The parameters in Ctorus_L.fits should also be linked to those in Ctorus_T in most cases.
An example is shown in Ctorus_test.xcm.


Keith Arnaud, Lab. for High Energy Astrophysics, NASA/Goddard Space Flight Center

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