Variation in the spiral pitch angle of the intrinsic polarization angles along the azimuthal angle in the ring between 4 kpc and 10 kpc radius in the plane of the galaxy, derived from the robust 2 data at 32″ × 26″ resolution. Sectors start at 0° on the south-eastern major axis of the galaxy on the plane of the sky and increase counter-clockwise. The errors were estimated from the standard deviations of Q and U values within each sector.