The role of kink instability in Poynting-flux dominated jets

The role of kink instability in magnetically driven jets is explored through numerical one-dimensional steady relativistic MHD calculations. The instability is shown to have enough time to grow and influence the dynamics of Poynting-flux dominated jets. In the case of AGN jets, the flow becomes kinetic flux dominated at distances greater than or similar to 1000 r(g) because of the rapid dissipation of Poynting flux. When applied to GRB outflows, the model predicts more gradual Poynting dissipation and moderately magnetized flow at distances of similar to 10(16) cm where the deceleration of the ejecta due to interaction with the external medium is expected. The energy released by the instability can power the compact "blazar zone" emission and the prompt emission of GRB outflows with high radiative efficiencies.