Collimation and Radiative Deceleration of Jets in TeV AGNs

TL;DR

This paper proposes a model where radiative cooling causes relativistic jets in TeV AGNs to recollimate, explaining rapid variability and flares observed at large distances from the central engine.

Contribution

It introduces a jet focusing model based on radiative cooling that accounts for rapid variability and recollimation in TeV AGNs, including M87 and blazars.

Findings

Radiative cooling can induce jet recollimation in small cross-sectional regions.

The model explains rapid variability observed in M87's HST-1 knot.

It accounts for rapid TeV flares with low Doppler factors in blazars.

Abstract

We consider some implications of the rapid X-ray and TeV variability observed in M87 and the TeV blazars. We outline a model for jet focusing and demonstrate that modest radiative cooling can lead to recollimation of a relativistic jet in a nozzle having a very small cross-sectional radius. Such a configuration can produce rapid variability at large distances from the central engine and may explain recent observations of the HST-1 knot in M87. Possible applications of this model to TeV blazars are discussed. We also discuss a scenario for the very rapid TeV flares observed with HESS and MAGIC in some blazars, that accommodates the relatively small Doppler factors inferred from radio observations.