Time dependent modelisation of TeV blazars by a stratified jet model

TL;DR

This paper introduces a new time-dependent, stratified jet model for TeV blazars that accounts for particle acceleration, cooling, and pair production, successfully reproducing observed spectra and flares with lower Lorentz factors.

Contribution

The model incorporates inhomogeneous jet stratification and a pile-up particle distribution, enabling realistic simulations of blazar emissions and flares with reduced Lorentz factors.

Findings

Successfully reproduces the broad band spectrum of PKS 2155-304

Simulates TeV flare light curves with Lorentz factor below 15

Highlights importance of pair production in jet emission modeling

Abstract

We present a new time-dependent inhomogeneous jet model of non-thermal blazar emission. Ultra-relativistic leptons are injected at the base of a jet and propagate along it. 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 PKS 2155-304 and its big TeV flare observed in 2006, we can reproduce simultaneously the average broad band spectrum of this source from radio to TeV, as well as TeV light curve of the flare with bulk Lorentz factor lower than 15.