Observed profiles (in black) of the polarization angle, the polarized intensity, and the polarization fraction, from top to bottom. The dashed blue curves show the variation of the background values of ψ_bg, P_bg, and p_bg derived from I_bg, Q_bg, and U_bg. On the middle three plots, the P_fil profiles in purple are derived from the polynomial fits I_fil, Q_fil, and U_fil. On the top and bottom plots, the horizontal purple lines indicate the mean values of the intrinsic polarization angle and fraction of the filaments for | r | ≤ R_out.