Mean (left) and standard deviation (right) of the B-mode power spectra (as computed by X²Pure) of 100 noise only simulations for different input maps. “Biased” refers to the biased map estimator defined in Eq. (25). The other lines refer to different maps derived from the unbiased map estimator Eq. (22). The value in the legend is the α parameter that quantifies the amount of map domain filtering applied to the unbiased map. Higher values of α correspond to more aggressive filtering, see Sect. 6.3.1 for more details.