Fake versus real data difference spectra. The magenta points show the double difference power spectrum of actual data (as in Fig. 3). The green line shows the same double difference spectrum computed from the ILC + 857 dust template maps described in the text. This model provides a good match to the magenta points both in amplitude and phasing. The blue points show the difference of the 217 and 143 power spectra for mask1, which adds CMB cosmic variance, illustrating why we use double-differenced spectra for this comparison. In all cases, the smoothed dust power spectrum model of Eq. (9) (with slightly adjusted amplitude to bring the residuals at these low multipoles close to zero) has been subtracted.