Left panel: result of the difference between the polarization angle map and a purely centro-symmetric pattern. Right panel: the top left image is a magnified version of the left panel, around the central source and top right is the result of the same processing on the K′ band angle map. The bottom right image is a magnified version of the degree of linear polarization found in Fig. 1, on which we overlaid the direction of the polarization vectors, showing the clear patch of aligned vectors in this region in the data before the subtraction of the centro-symmetric pattern.