A Two Zone Synchrotron Model for the Knots in the M87 Jet
  The flux and the spectral index in X-ray energy band from the knots of M87 jet as observed by {\it{Chandra}} indicate a possible synchrotron origin but cannot be explained by simple one zone models with continuous injection of non-thermal electrons. In this letter we propose a two-zone model to explain the observed spectra of the knots of M87 jet. We consider the synchrotron emission from a region with tangled magnetic field where relativistic non-thermal electrons are continuously injected in from an associated acceleration region. The acceleration region is assumed to be compact zone possibly around a shock front. A power-law distribution of electron is injected into the acceleration region and are accelerated to a maximum energy determined by the acceleration time scale and the loss processes. With the present model we are able to explain the overall broadband features of the knots of M87 jet. Also the present model predicts a change in spectral index at ultraviolet energies and future observations at these energies can be used to constrain the parameters involved in the model. 
S. Sahayanathan