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It is now well known that most astrophysical objects are associated with quasi-steady mass outflows. Recently, optical and ultraviolet observations of stellar atmospheres showed mass outflow from both hot and cool stars. High resolution images by radio and optical observations of radio galaxies (active galactic nuclei - AGN), and quasars have shown the presence of collimated jets. Furthermore, radio and infrared observations of star forming regions (young stellar objects - YSO) also have shown the existence of outflows.
There are theoretical reasons for postulating that the AGN jets are relativistic outflows (Lorentz gamma $>$ 5) initiated on scales of order $r_{g} = GM/c^{2} = 1.5 \time 10^{13}$ Mgcm. From models of central engines (massive black holes) the jet energy may be extracted electromagnetically from the black holes and the jet plasma believed to be electron-positron pairs.
The most approaches used to explain the above physical mechanisms of the driving and collimation processes are theoretical works and simulation works using hydrodynamic as well as MHD models. However, in order to understand the coherent radiation from the pulsar wind, active galactic nuclei jets, radio galaxy jets, and protostellar jets, it is necessary to use a particle code. We will use a fully relativistic, electromagnetic particle code to simulate wave-particle interactions which are essential for understanding the wave-driven mechanism in jets.
Recently we have investigated nonlinear Alfv\'{e}n waves driven by an nonrelativistic and relativistic electron beam in an electron-positron plasma by using a 3-D relativistic electromagnetic particle code. As an extension of this work we have started to investigate a coherent radiation from jets. The simulation studies will help us understand kinetic effects of evolution of jets and associated radiations.
