First (left panels) and second (right panels) principal components of variability. The upper panels show the spectra corresponding to the maximal and minimal coordinate α_j,k over the j = 10 observations of the first (k = 1, left) and second (k = 2, right) eigenvectors. The middle panels show the ratio of the maximum and minimum spectra to the total spectrum of the source. The bottom panels show the contribution of each component to the total variance as a function of energy.