6 Conclusion

Observational and theoretical arguments suggest that astrophysical jets should exhibit intrinsic rotation of material perpendicular to the jet axis. Motivated by such arguments, we have proposed and analysed a basic model for the acceleration of energetic particles by centrifugal and viscous shear effects which is applicable to relativistic, intrinsically rotating jet flows. The results obtained indicate that particle acceleration in rotating jets might represent an active mechanism for the production of the synchrotron-emitting high energy particles by giving rise to power law particle momentum distributions over a wide range of conditions. Due to its anticipated non-localized operation, such a mechanism is expected to be of particular relevance for the explanation of the recently observed extended emission in the jets from AGN. Moreover, as a general mechanism this process is able to provide high energy particles, which are required as seed particles for the (localised) first-order Fermi acceleration widely believed to occur in relativistic jets (e.g. Drury 1983; Kirk & Duffy 1999). Particularly, in the beginning the injection of seed particles could naturally occur at the base of the jet due to centrifugal acceleration (cf. Rieger & Mannheim 2000).

Acknowledgements

We would like to thank C. Hettlage and D. Rieger for a careful reading of the manuscript. Useful discussions with S. Jester and M. Ostrowski and helpful comments by an anonymous referee are gratefully acknowledged. F.M.R. acknowledges support from the German Deutsche Forschungsgemeinschaft (DFG), project number MA 1545/2-2.