Left: Monte Carlo simulations of transmitted AGN spectra through a toroidal obscuring material with variable density profile (see right panel). The Monte Carlo simulations include both photoelectric absorption and Compton scattering. The intrinsic AGN spectrum is a power-law. The different colours indicate X-ray spectra observed at different zenith distances. Right: Cross-section of the toroidal geometry used to produce the simulated spectra shown in the left panel. The The torus is azimuthally symmetric and the density changes along the zenith angle as indicated by the shading of the different slices. At 90° the equivalent hydrogen column density of the torus is 10²⁴cm^-2. More details can be found here.

Observations have shown the presence of gas and dust clouds around Active Galactic Nuclei (AGN) that both absorb and scatter the radiation emitted by the accretion process and therefore modify the observed Spectral Energy Distribution of these sources. It is also suggested that the overall geometry of the obscuring material can be approximated by a toroidal shape, although in detail the structure of the obscurer is likely to be complex, dynamically variable and possible related to the accretion process itself. This complexity is imprinted in the X-ray spectra of AGN, which show emission components associated with both line-of-sight obscuration and scattering from dense material outside the line-of-sight. This highlights the importance of physically motivated models for the obscurer to interpret the X-ray spectra of AGN.

Monte Carlo simulations are currently in progress to produce model X-ray spectra of AGN assuming transmission through an obscuring material with toroidal geometry and a variable density profile, i.e. similar to that suggested by recent hydrodynamic simulations of AGN tori. These simulated X-ray spectra can be used to model the observed X-ray spectra of AGN to infer physical parameters as well as population properties and also reconstruct the diffuse X-ray background radiation