Intensity (left), Stokes Q (center) and U (right) maps, for a uniform unpolarized disk of unitary surface brightness and radius equal to 15 arcses (upper panel) assuming for the geometrical PSF the one given by Fabiani et al. (2014) at 2.95 keV, and taking σ_f = 1 arcsec (recall that Q and U scales as ). Axis are in arcsec, reference frame is chosen such that Q is positive for polarization aligned along the x-axis. The bottom panel shows the same as the top, but for a uniform unpolarized ring with an outer radius equal to 15 arcses and inner one equal to 10 arcsec.