We consider neutralino annihilation in dense extragalactic systems known to be dominated by dark matter, in particular M87 and several local dwarf spheroidal galaxies. These annihilations can produce energetic gamma rays which may be visible to atmospheric Čerenkov telescopes. We explore the supersymmetric parameter space, and compute the expected flux of gamma rays coming from these objects. It is shown that some parts of the parameter space lead to a signal observable with the next generation of Čerenkov telescopes, provided the supersymmetric dark matter has a clumpy structure, as may be expected in a hierarchical scenario for structure formation.

• Received 7 September 1999

DOI:https://doi.org/10.1103/PhysRevD.61.023514