Top panel: Reddening-corrected total flux of Mrk 231. Second panel: Polarized flux of Mrk 231, established from the multiplication of the flux and the polarization degree. Third panel: Linear polarization degree. Bottom panel: Polarization position angle of Mrk 231. The aperture is color-coded (in arcseconds). The gray zone represents the waveband in which we observe the cut-off in the UV spectrum, associated with a strong rise in the degree of polarization and a distinctive rotation in the polarization position angle. The data used to construct those plots are the one summarized in Table 1. The data highlighted in red as the new ones we derived from the poorly explored HST/FOC observation of Mrk 231.