Left: power spectra (PSs) of the X-ray surface brightness (SB) fluctuations in the Perseus Cluster in the central 3 arcmin (purple) and in the annulus 3–10.5 arcmin (orange). Dash curves: the initial PS. Dotted regions: PS of the Poisson noise. Dash–dotted curves: PS of the combined Chandra PSF in both analysed regions. Hatched region with filled boundaries: PS of the SB fluctuations after subtraction of the Poisson noise. Both statistical (1σ) and stochastic uncertainties are taken into account. Notice, that very high statistics of counts accumulated by the 1.4 Ms observations allows us to probe fluctuations on a broad range of length-scales, from >100 kpc down to few kpc (comparable with the mean free path). Right: amplitude of the SB fluctuations in the same regions, obtained from the PS corrected for the PSF (see Section 4). Notice, that the amplitude of fluctuations varies with the radius. For these two regions a maximal difference by a factor of 4 is reached on ∼17 kpc scale.