Planck primordial power spectrum feature search results. Top four panels: the reconstructed power spectrum at four values for the smoothing parameter λ. The red curves indicate the maximum likelihood configuration for the fractional deviation f(k) of the power spectrum relative to a power law fiducial model (with A_s = 2.20 × 10^-9 and n_s = 0.9603) for the penalized likelihood. The error bars have a width corresponding to the minimum reconstructible width (the minimum width for a Gaussian feature so that the mean square deviation of the expectation value of the reconstruction differs by less than 10%) and a vertical extent showing the 1σ and 2σ limits for the fractional deviation averaged over the box. The grey hashed regions at the far left and right show where the fixing prior (i.e., α) sets f(k) = 0. The inner grey regions show where the reconstruction bias is so great that the minimum reconstructible width is undefined. Mock features in this region produce reverberations over the entire interval. With λ = 10³ and λ = 10⁴, we find statistically significant fluctuations around k ~ 0.1 Mpc^-1. Lower panels: the 1σ error bars for three combinations of cosmological parameters at the four values of λ. The maximum likelihood value for the fiducial model is indicated by the dashed line for comparison.