Eigenvalue–fraction diagram of the XMM-Newton EPIC-pn+MOS2 (top), Chandra ACIS-S X1 (middle), and X2 (bottom). The normalized fraction variability values of PCA components are plotted against the corresponding eigenvector orders. The linear regression among logarithmic fractional eigenvalues starting from three onward is also plotted (gray line). The number of nonzero eigenvalues in each diagram corresponds to the number of time-sliced spectra. The spectra and time series of the PCA components (color circles), which are statistically significant, are plotted with the same colors in Figure 5.