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   81709
   High Frequency Peaked BL Lac objects emit X-ray synchrotron radiation.
   The required high energies of the radiating electrons indicate very
   efficient particle acceleration in the relativistic jets of these
   sources. Long term and uninterrupted monitoring is the only approach
   for quantitative investigation of the extreme physical conditions in
   those regions in the jet where the high-energy radiation is emitted. We
   propose to observe five bright objects, in which X-rays are due to
   Synchrotron emission by the high energy end of the electron
   distribution.
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