Top panel: photon–photon absorption correction to be applied to the M 87 spectrum for three IR EBL adopted intensities. The intermediate curve corresponds to the FR2017, and the upper and lower curves to IR EBL intensities a factor two higher and lower between 10 and 100 μm. Bottom panel: as in Fig. 6, for the three IR EBL models. The 50-h 5σ and 100-h 2σ sensitivity limits for CTA, and the HAWC and LHAASO five-year 5σ limits are also indicated.