Parameter p₀ (top) and slopes of the EE (middle) and BB (bottom) power spectra of stage b maps vs. the slope α_M of the power spectrum of the turbulent component of the magnetic field (left) and vs. the relative strength of the turbulence f_M (right). In the left plots f_M = 0.8 and in the right plots α_M = −2.5. Red stars (blue squares) represent results for N = 4 (N = 7). The abscissae of the two sets of points are slightly shifted from their original values for a better visibility. The values observed in the data are represented by a gray shaded region for α_EE and α_BB (a dashed line for the mean, dark, and light gray for the 1- and 2σ uncertainties) and by a hatched regions for p₀ (a dashed horizontal line for the mean, and a red 45° (resp. blue −45°) hatched region for 1σ uncertainty for N = 4 (resp. 7)).