Emission from an inhomogeneous mound with kT_e = 5 keV and B ∼ 3.6 × 10¹² G (E_cyc = 40 keV). Top: flux for the cases including the plasma and vacuum polarization effects for non-adiabatic,“non-ad” and adiabatic, “ad”, mode propagation (left) and the pure plasma and vacuum cases (right). The left top panel shows the corresponding blackbody spectrum (“BB”). Bottom: corresponding degree of polarization. The energy range accessible by the Imaging X-ray Polarimetry Explorer (IXPE) is shown by the light blue transparent region.