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   PR # 11014
    We propose observations of four samples of middle-aged (10^4 yr)
    pulsars.  Middle-aged pulsars have large spin-down luminosity, and
    hence are ideal to study the emission mechanism of high energy radiat
    ions, which is the best diagnostic of pulsar wind.  Pulsar models are
    now sophisticated enough to warrant comparision with observations.The
    pulsar wind terminates into a synchrotron nebula, the plerion. Observ
    ations of the plerionic emission is our best way to probe the evolut-
    ion of pulsar wind from light cylinder to nebular scales. The study
    of the evolution of plerions has considerable bearing to the topic of
    pulsar-SNR associations. Some young pulsars do not appear to have a
    bright plerion.  Observations of the middle-aged pulsar are essential
   to understand evolution of ple
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