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Measurements of the gamma ray flux from a number of supernova remnants (SNRs) at energies above 250 GeV have been made with the Whipple Imaging air \v Cerenkov detector. Observation of the gamma ray emission of SNRs at energies above 1~GeV should provide a sensitive test of shock acceleration models of particle acceleration in SNRs. Gamma-ray luminosities of supernova remnants are well constrained by the observed supernova rate and the cosmic ray flux if supernovae are indeed the source of cosmic rays. Drury et al. (Astron.~Astrophys.~287 , 959 (1994)) predict that the luminosity of nearby Sedov-phase SNRs should be observable by the Whipple telescope. In this model, diffusive shock acceleration produces energetic charged particles which interact with the ambient medium forming gamma rays. There is an indication that a number of unidentified EGRET sources may correspond to supernova remnants (G.~Kanbach, private communication), although at these energies ($>$100 MeV) the diffuse background is somewhat uncertain. Measurements of the gamma-ray flux with the Whipple instrument have a similar sensitivity to the EGRET detector for a source spectral index of $2.15$, and less sensitivity to diffuse background. A number of observations of SNRs including: Tycho, W66, IC443, and others have been made. Currently for Tycho an upper limit of 9$\times 10^{-12}$cm$^{-2}$sec$^{-1}$ is obtained. The status of these observations will be presented, and it will be shown that these measurements combined with the EGRET observations are beginning to provide a useful constraint on models of cosmic ray origin. Gamma-ray observations may also be used to constrain models of particle acceleration in SNRs exhibiting pulser-powered synchrotron nebula (plerions). The status of observations of this class of objects, including the Crab nebula, will also be presented.
Supported in part by the U.S.~Dept.~of Energy.
