TeV blazar variability: the firehose instability?

TL;DR

This paper proposes that the firehose instability caused by pressure anisotropy in blazar jets can explain the minute-scale TeV variability observed in certain blazars, aligning theoretical growth timescales with observations.

Contribution

It introduces a jet instability mechanism, the firehose instability, as a plausible explanation for rapid TeV variability in blazars, linking plasma physics with observational data.

Findings

Firehose instability growth timescale is a few minutes.

The instability can cause jet disruptions leading to observed variability.

Results match observed TeV variability timescales for specific blazars.

Abstract

Recently observed minute timescale variability of blazar emission at TeV energies has imposed severe constraints on jet models and TeV emission mechanisms. We focus on a robust jet instability to explain this variability. As a consequence of the bulk outflow of the jet plasma, the pressure is likely to be anisotropic, with the parallel pressure $P_{||}$ in the forward jet direction exceeding the perpendicular pressure $P_{\perp}$. Under these circumstances, the jet is susceptible to the firehose instability, which can cause disruptions in the large scale jet structure and result in variability of the observed radiation. For a realistic range of parameters, we find that the growth timescale of the firehose instability is $\approx$ a few minutes, in good agreement with the observed TeV variability timescales for Mrk 501 (Albert et al. 2007) and PKS 2155-304 (Aharonian et al. 2007).