Abstract
We model the acceleration of energetic particles due to shear and centrifugal effects in rotating astrophysical jets. The appropriate equation describing the diffusive transport of energetic particles in a collisionless, rotating background flow is derived and analytical steady state solutions are discussed. In particular, by considering velocity profiles from rigid, over flat to Keplerian rotation, the effects of centrifugal and shear acceleration of particles scattered by magnetic inhomogeneities are distinguished. In the case where shear acceleration dominates, it is confirmed that power law particle momentum solutions $f(p) \propto p^{-(3+\alpha)}$ exist, if the mean scattering time $\tau_c \propto p^{\alpha}$ is an increasing function of momentum. We show that for a more complex interplay between shear and centrifugal acceleration, the recovered power law momentum spectra might be significantly steeper but flatten with increasing azimuthal velocity due to the increasing centrifugal effects. The possible relevance of shear and centrifugal acceleration for the observed extended emission in AGN is demonstrated for the case of the jet in the quasar 3C273.
Highlights
Astrophysical jets emerge from a variety of astrophysical sources, ranging from protostellar objects, to micro-quasars, active galactic nuclei (AGN) and probably Gamma Ray Bursts (GRBs)
Observational and theoretical arguments suggest that astrophysical jets should exhibit intrinsic rotation of material perpendicular to the jet axis
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
Summary
Astrophysical jets emerge from a variety of astrophysical sources, ranging from protostellar objects, to micro-quasars, active galactic nuclei (AGN) and probably Gamma Ray Bursts (GRBs). The observations of jets from radio-loud AGN may be counted among the most interesting ones as they constitute test laboratories for studying the spatial structure in relativistic jets. Today there is convincing evidence that the central engine in these AGN is a rotating supermassive black hole surrounded by a geometrically thin accretion disk, which gives rise to the formation of a pair of relativistic jets. Models based on the assumption of a one-dimensional velocity structure have allowed useful insights into the emission properties of AGN jets. As real jets are generally expected to show a significant velocity shear perpendicular to their axes, such models may be adequate only for a first approximation. Several independent arguments suggest that AGN jet flows might be characterized by an additional rotational
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