Structure function for the NOEMA calibrator (top), the NOEMA (middle), and NuSTAR (bottom) observations of MCG+08-11-11. The solid line is the best linear log–log fit, and the corresponding slopes (with the corresponding errors) are indicated in each figure. The vertical dotted line in the middle plot indicates a local maximum around τ = 2 × 10⁴ s. The dashed line corresponds to the cubic polynomial best fit (in log scale), which was used to plot the data/model ratio in Fig. 4.