Reflection spectra of thick accretion discs

ABSTRACT Relativistic reflection features are commonly observed in the X-ray spectra of stellar-mass and supermassive black holes and originate from illumination of the inner part of the accretion disc by a hot corona. All the available relativistic reflection models assume that the disc is infinitesimally thin and the inner edge is at the innermost stable circular orbit or at a larger radius. However, we know that several sources, especially among supermassive black holes, have quite high-mass accretion rates. In such a case, the accretion disc becomes geometrically thick and the inner edge of the disc is expected to be inside the innermost stable circular orbit. In this work, we employ the Polish donut model to describe geometrically thick discs and we study the iron-line shapes from similar systems. We also simulate full reflection spectra and we analyse the simulated observations with a thin disc relativistic reflection model to determine the impact of the disc structure on the estimation of the model parameters, in particular in the case of tests of the Kerr hypothesis.

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