Discrepancies in AGN Corona Height Measurements: Insights from X-ray and Optical Studies

Hard X-ray emission in AGN originates from a compact region known as the hot corona, although its precise geometry remains unclear. It is often modeled as a 'lamp-post', where the source is compact and either point-like or spherical, positioned along the symmetry axis above the equatorial plane. Spectral and light echo studies, conducted in both the X-ray and optical domains, are commonly used to estimate the height and size of this hot corona. In our analysis, we have compiled a sample of AGN sources with height determinations from both spectral bands. Interestingly, the average height derived from X-ray studies (~13 Rg) is significantly smaller compared to that from optical studies (~32 Rg). This discrepancy could stem from differences in source selection between the two types of studies or from the sensitivity of the methods employed. Investigating this issue further is one of the key projects proposed for the Polish-Czech collaboration.