RADIO SUPERNOVAE AS TEV GAMMA-RAY SOURCES

When applied to the blast wave formed by the explosion of a massive st ar as a supernova (SN), the theory of diffusive particle acceleration at shock fronts predicts a very high energy density in cosmic rays. Al most immediately after particles begin to be injected into the process , the cosmic ray pressure rises until comparable to the ram-pressure e ncountered by the shock front. Those supernovae which are observed in the radio band i.e., radio supernovae (RSNe), provide direct evidence of particle acceleration in the form of synchrotron emitting electrons . Furthermore, these objects are particularly interesting, since they are usually surrounded by a relatively dense confining medium. The acc eleration of cosmic rays can then lead to the production of very high energy (VHE) gamma-rays which arise from collisions between energetic particles and target nuclei. We estimate the cosmic ray energy density assuming a fraction phi less than or similar to 1 of the energy avail able at the shock front is converted into cosmic rays. Combining this with the parameters describing the environment of the SN progenitor, a s deduced from observations, and from more detailed modelling, we comp ute the flux at Earth F(> 1 TeV) of photons of energy above 1 TeV. For the relatively weak but nearby supernova SN1987A we predict F(> 1 TeV ) = 2 x 10(-13) photons s(-1) cm(-2) before the shock front encounters the ring of dense matter seen by the Hubble Space Telescope. Subseque ntly, the flux is expected to rise further. The medium around SN1993J in M81 is thought to have a density profile rho proportional to tau(-3 /2), (with tau the distance from the point of explosion) for which we predict a roughly constant flux of F(> 1 TeV) = 2 x 10(-12) photons s( -1) cm(-2). Once the shock emerges into the region where rho proportio nal to tau(-2), which is expected at larger distances, the flux should decrease in proportion to t(-1). This object thus presents an interes ting target for observation by telescopes which detect the Cerenkov li ght emitted by the air showers from VHE photons. A detection would pro vide observational confirmation of cosmic ray acceleration in supernov ae.