Fast TeV variability in blazars: jets in a jet

TL;DR

This paper proposes a model where fast TeV variability in blazars is caused by compact regions within jets moving relativistically, powered by magnetic reconnection in Poynting flux-dominated jets, explaining rapid flares.

Contribution

It introduces a novel jet-in-a-jet model involving magnetic reconnection to explain rapid TeV variability in blazars, differing from previous models.

Findings

Relativistically moving compact regions can produce observed TeV flares.

Magnetic reconnection efficiently powers TeV emission via synchrotron-self-Compton.

Model predicts simultaneous UV/X-ray flares.

Abstract

The fast TeV variability of the blazars Mrk 501 and PKS 2155--304 implies a compact emitting region that moves with a bulk Lorentz factor of Gamma_{em}~100 toward the observer. The Lorentz factor is clearly in excess of the jet Lorentz factors Gamma_j\simless 10 measured on sub-pc scales in these sources. We propose that the TeV emission originates from compact emitting regions that move relativistically {\it within} a jet of bulk Gamma_j~10. This can be physically realized in a Poynting flux-dominated jet. We show that if a large fraction of the luminosity of the jet is prone to magnetic dissipation through reconnection, then material outflowing from the reconnection regions can efficiently power the observed TeV flares through synchrotron-self-Compton emission. The model predicts simultaneous far UV/soft X-ray flares.