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X-ray observations suggest high compactness of coronae in active galacticnuclei as well as in X-ray binaries. The compactness of the source implies astrong radial dependence in the illumination of the accretion disc. This will,for any reasonable radial profile of the density, lead to a radial profile ofthe disc ionisation. Svoboda et al. (2012) showed on a single example thatassuming a radially-structured ionisation profile of the disc can cause anartificial increase of the radial-emissivity parameter. We further investigatehow the X-ray spectra are modified and quantify this effect for a wide range ofparameters. Computations are carried out with the current state-of-the-artmodels for relativistic reflection. We simulated spectra using the responsefiles of the micro-calorimeter X-IFU, which is planned to be on board ofAthena. We assumed typical parameters for X-ray bright Seyfert-1 galaxies andconsidered two scenarios for the disc ionisation: 1) a radial profile for thedisc ionisation, 2) a constant disc ionisation. We found that steep emissivityprofiles can be indeed achieved due to the radial profile of the discionisation, which becomes more important for the cases where the corona islocated at low heights above the black hole and this effect may be even moreprominent than the geometrical effects. We also found that the cases with highinner disc ionisation, rapidly decreasing with radius, may result in aninaccurate black hole spin measurements.

Steep X-ray reflection emissivity profiles in AGN as the result of radially-structured disc ionisation