Résumé
Already in the first days after the explosion of a supernova, the strong shock expanding forward into the dense wind of the progenitor star can theoretically accelerate particles up to the ~PeV (=1015 eV) range. These accelerated particles, interacting with the dense wind material, should lead to the production of gamma-rays in the 1–100 TeV range, through pion production. However, no supernova has yet been detected by current Cerenkov instruments, and the question of the detectability of extragalactic supernovae in nearby galaxies (within a few Mpc) by next generation instruments is still open. The detection in the TeV range is especially hindered by the two-photon annihilation process, in which high-energy gamma-rays interact with soft photons from the photosphere to produce electron/positron pairs, thereby degrading the gamma-ray signal from the system. We calculate the temporal evolution of the expected gamma-ray attenuation in the well-studied type IIb SN 1993J, accounting for both temporal and geometrical effects.