Recollimation and Radiative Focusing of Relativistic Jets: Applications to Blazars and M87

Understand

Recent observations of M87 and some blazars reveal violent activity in small regions located at relatively large distances from the central engine.

• Motivated by these considerations, we study the hydrodynamic collimation of a relativistic cooling outflow using a semi-analytical model developed earlier.
• We first demonstrate that radiative cooling of the shocked outflow layer can lead to a focusing of the outflow and its reconfinement in a region having a very small cross-sectional radius.
• Such a configuration can produce rapid variability at large distances from the central engine via reflections of the converging recollimation shock.