A direct comparison of X-ray spectral models for tori in active galactic nuclei

Abstract

Several X-ray spectralmodels for tori in active galactic nuclei (AGNs) are available to constrain the properties of tori; however, the accuracy of these models has not been verified. We recently constructed a code for the torus using GEANT4, which can easily handle different geometries. Thus, we adopt the same assumptions as Murphy & Yaqoob (2009, MNRAS, 397, 1549) and Brightman & Nandra (2011, MNRAS, 413, 1206) and try to reproduce their spectra. As a result, we can reproduce well the reflection spectra and the strength of the Fe Kα line of Murphy & Yaqoob, for both NH = 1024 and 1025 cm-2. However, we cannot produce the strong reflection component of Brightman & Nandra in the low-energy band. The origin of this component is the reflection from the visible inner wall of the torus, and the reflection should be very weak in the edge-on directions under the geometry of Brightman & Nandra. Therefore, the behaviour of the reflection spectra in Brightman & Nandra is not consistent with their geometry. The strength of the Fe Kα line of Brightman & Nandra is also different from our results and the analytical result in the optically thin case. The limitation of the spectral model will bias the parameters from the X-ray spectral fitting.