Gamma-ray luminosities in the Fermi-LAT energy range (dashed) and H.E.S.S. energy range (solid) accounting for γγ absorption. Top: SNR of LBV progenitors interacting with the dense shell at different times (models as described in Table 1). The γγ absorption has ceased completely after about 200 days. Bottom: interaction of SNRs with RSG progenitors interacting with dense shells created by external photoionization. The purple case represents an upper limit in terms of shell mass, cause by a high mass-loss wind and a strong ambient photon field. The diluted case represents typical parameters for the population of RSGs (see Table 1 for details).