Maps of I, U and Q for a point source computed according to Eqs. (28)–(30) with functions 𝒢(r) and 𝒦(r), fitted on a GEANT4 simulation of an unpolarized point source (upper panels). The same is shown in the lower panels, but for functions 𝒢(r) and 𝒦(r) fitted on the Cygnus X-1 observation by the IXPE satellite. The reference frame is chosen such that Q is positive for polarization aligned along the x-axis.