Abstrakt
We study the theoretical spectrum and polarisation properties of X-ray emission from accretion discs in active galactic nuclei (AGN). The reflected radiation from an accretion disc illuminated by a corona above is computed using the Monte Carlo radiative transfer code STOKES.
The structure of the disc, modelled as a constant density slab, has been computed with the TITAN code for optically thick and hot photo-ionized media. The resulting simulated spectra locally emitted by the accretion disc in 0.1-100 keV energy band are compared to the results obtained by various, published radiative transfer codes.
In addition to these, the STOKES code provides also the polarisation degree and polarisation position angle of the outcoming radiation that depend on the geometry of scattering and other key parameters such as the ionisation of the disc. Further, we use the relativistic code KYNSTOKES based on our well-tested relativistic KY package to account for all relativistic effects on radiation near a black hole and to compute the total disc emission as would be detected by a distant observer.
It is then possible to predict X-ray spectral and polarisation properties of an accretion disc in AGN and their dependence on various parameters of the system (spin of the black hole, ionization of the accretion disc, observer inclination). This is fundamental for the interpretation of AGN spectra and polarisation obtained by the NASA IXPE mission or the Chinese-lead eXTP mission.