Temporal spectrum , as a function of the reduced frequency . The data points (in orange) have been binned according to the value of (which depends on both ω and k), and only the mean over each bin is shown. These data points collapse onto a unique, slowly varying curve, which was adjusted alternatively with a Gaussian function (Eq. (50), solid black line) and a Lorentzian function (Eq. (51), solid green line). The latter is clearly the best fit, obtained for an amplitude A = 1.85 and a standard deviation σ = 0.62.