Reflection Spectra from a Thin Disc Model with Finite Thickness and Its Application to X-ray Spectral Data

The accretion disc around a black hole is illuminated by the hot X-ray corona and produces a reprocessed spectrum on its surface, which is often referred to as the disc ‘reflection’ spectrum. The disc reflection encodes information such as the geometry of the innermost accretion which can be uncovered by modelling.

Previous disc reflection models assumed a simple thin disc model with infinitely small height for simplification. Some previous works often adopt the standard thin disc model, in which the thickness of the disc is comparable to the size of the corona in AGN measured by reverberation. So disc geometry must play an essential role in disc reflection modelling. There have been only a few attempts to fit the X-ray data of AGN using a model with finite disc thickness because of the difficulty of modelling more complex geometries and the limited spectral resolutions in X-ray CCD data. I will demonstrate the systematic uncertainties in measuring accretion geometry by fitting observational data of MCG-6-30-15 using a new thin disc model with finite thickness. In the end, I will also discuss how future microcalorimeter-resolution data, e.g. from XRISM and Athena, will improve our measurements of accretion geometry using disc reflection spectroscopy.