Radiative Collimation of Electron–Positron Jets

Abstract

Abstract We propose a novel mechanism for the collimation of relativistic outflows emanated from accretion disks via the disk radiation field, itself. In general, winds driven by disk radiation fields diverge, due to the effect of rotation and the nature of radiation. If, however, the disk is divided into an optically thin hot inner region and an optically thick luminous outer region, the outflow ejected from the inner disk is accelerated and collimated by radiation fields produced by the outer disk. Since this mechanism effectively works on electron–positron pair plasmas, in accretion disk systems with inner hot advection-dominated regions, electron–positron jets easily form on the disk-rotation axis. For pure electron–positron pair plasmas, the terminal speed of collimated jets is about $0.9c$, which is very close to the jet speed of galactic superluminal sources.