Locus of the time evolution of 1 − 10 TeV and 20 − 100 TeV emission in surface brightness and photon index, for typical SNR-PWN system M2 (see Table 1) and four variants with modified particle injection spectrum. Both panels correspond to a calculation with particle escape across the system. Model-predicted emission is compared to data from the HGPS and LHAASO catalogues (WCDA for the 1 − 10 TeV band and KM2A for the 20 − 100 TeV band). Stars indicate the starting point of each track.