Planck HFI 353 GHz (red, top) and (blue, bottom) power spectra (in μK) computed on three of the selected LR analysis regions that have f_sky = 0.3 (circles, lightest), f_sky = 0.5 (diamonds, medium) and f_sky = 0.7 (squares, darkest). The uncertainties shown are ± 1σ. The best-fit power laws in ℓ are given for each spectrum as a dashed line of the corresponding colour. The Planck 2013 best-fit ΛCDM expectation (Planck Collaboration XVI 2014) and the corresponding r = 0.2 CMB model are shown as solid black lines; the rise for ℓ> 200 is from the lensing contribution. In the lower parts of each panel, the global estimates of the power spectra of the systematic effects responsible for intensity-to-polarization leakage (Sect. 2.3) are shown in different shades of grey, with the same symbols to identify the three regions. Finally, absolute values of the null-test spectra anticipated in Sect. 2.3, computed here from the cross-spectra of the HalfRing/DetSet differences (see text), are represented as dashed-dotted, dashed, and dotted grey lines for the three LR regions.