paper

Recollimation shocks and radiative losses in extragalactic relativistic jets

arXiv:1710.06713 · doi:10.1051/0004-6361/201732000

Abstract

We present the results of state-of-the-art simulations of recollimation shocks induced by the interaction of a relativistic jet with an external medium, including the effect of radiative losses of the shocked gas. Our simulations confirm that -- as suggested by earlier semi-analytical models -- the post-shock pressure loss induced by radiative losses may lead to a stationary equilibrium state characterized by a very strong focusing of the flow, with the formation of quite narrow nozzles, with cross-sectional radii as small as times the length scale of the jet. We also study the time-dependent evolution of the jet structure induced of a density perturbation injected at the flow base. The set-up and the results of the simulations are particularly relevant for the interpretation of the observed rapid variability of the -ray emission associated to flat spectrum radio quasars. In particular, the combined effects of jet focusing and Doppler beaming of the observed radiation make it possible to explain the sub-hour flaring events such as that observed in the FSRQ PKS 1222+216 by MAGIC.

8 pages, 8 figures, Astronomy and Astrophysics accepted

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