An inhomogeneous jet model for the rapid variability of TeV blazars

TL;DR

This paper introduces a new inhomogeneous jet model for blazars that explains rapid TeV variability and spectral energy distribution with lower bulk Lorentz factors, incorporating particle reacceleration, Klein-Nishina effects, and pair production.

Contribution

The model combines inhomogeneous jet structure with a pile-up particle distribution to better reproduce blazar emission and variability, reducing the need for high Lorentz factors compared to previous models.

Findings

Successfully reproduces the spectrum and variability of PKS2155-304

Allows lower bulk Lorentz factors than one-zone models

Includes Klein-Nishina effects and gamma-gamma absorption

Abstract

We present a new time-dependent inhomogeneous jet model of non-thermal blazar emission, which reproduces the entire spectral energy distribution together with the rapid gamma-ray variability. Ultra-relativistic leptons are injected at the base of a jet and propagate along the jet structure. We assume continuous reacceleration and cooling, producing a relativistic quasi-maxwellian (or "pile-up") particle energy distribution. The synchrotron and Synchrotron-Self Compton jet emissivity are computed at each altitude. Klein-Nishina effects as well as intrinsic gamma-gamma absorption are included in the computation. Due to the pair production optical depth, considerable particle density enhancement can occur, particularly during flaring states. Time-dependent jet emission can be computed by varying the particle injection, but due to the sensitivity of pair production process, only small variations of the injected density are required during the flares. The stratification of the jet emission, together with a pile-up distribution, allows significantly lower bulk Lorentz factors, compared to one-zone models. Applying this model to the case of PKS2155-304 and its big TeV flare observed in 2006, we can reproduce simultaneously the average broad band spectrum of this source as well as the TeV spectra and TeV light curve of the flare with bulk Lorentz factor lower than 15.