Evolution of the spectral index and normalization over time when left free to vary. Top: evolution of (left) the amplitude normalization and (right) spectral index of HESS J1745-290 with time. Bottom: evolution of (left) the amplitude normalization and (right) spectral index of the DE with time. In each panel, the blue line shows the best-fit constant value with its associated uncertainty. The corresponding χ²/d.o.f. values are indicated, showing that in all cases the parameters are compatible with being constant.