Linking accretion flow and particle acceleration in jets-I. New relativistic magnetohydrodynamical jet solutions including gravity

Abstract

We present a new, approximate method for modelling the acceleration and collimation of relativistic jets in the presence of gravity. Thismethod is self-similar throughout the computational domain where gravitational effects are negligible and, where significant, self-similar within a flux tube. These solutions are applicable to jets launched from a small region (e.g. near the inner edge of an accretion disc). As implied by earlier work, the flow can converge on to the rotation axis, potentially creating a collimation shock. In this first version of the method, we derive the gravitational contribution to the relativistic equations by analogy with non-relativistic flow. This approach captures the relativistic kinetic gravitational mass of the flowing plasma, but not that due to internal thermal and magnetic energies. A more sophisticated treatment, derived from the basic general relativistic magnetohydrodynamical equations, is currently being developed. Here we present an initial exploration of parameter space, describing the effects the model parameters have on flow solutions and the location of the collimation shock. These results provide the groundwork for new, semi-analytic models of relativistic jets which can constrain conditions near the black hole by fitting the jet break seen increasingly in X-ray binaries. © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.