Synchrotron Self-Compton Analysis of TeV X-ray Selected BL Lacertae Objects

TL;DR

This paper presents a detailed synchrotron self-Compton modeling approach for TeV X-ray selected BL Lac objects, fitting multiwavelength data to derive jet parameters and understand high-energy emission mechanisms.

Contribution

It introduces a new methodology for analyzing multiwavelength data of XBLs, accurately modeling their spectra and inferring jet properties using a minimal set of parameters.

Findings

Doppler factors > 60 for PKS 2155-304 during a giant TeV flare

Jet powers exceeding 10^{46} erg/s for the same event

Doppler factors > 30 and jet powers > 10^{45} erg/s for Mkn 421 flare

Abstract

We introduce a methodology for analysis of multiwavelength data from X-ray selected BL Lac (XBL) objects detected in the TeV regime. By assuming that the radio--through--X-ray flux from XBLs is nonthermal synchrotron radiation emitted by isotropically-distributed electrons in the randomly oriented magnetic field of a relativistic blazar jet, we obtain the electron spectrum. This spectrum is then used to deduce the synchrotron self-Compton (SSC) spectrum as a function of the Doppler factor, magnetic field, and variability timescale. The variability timescale is used to infer the comoving blob radius from light travel-time arguments, leaving only two parameters. With this approach, we accurately simulate the synchrotron and SSC spectrum of flaring XBLs in the Thomson through Klein-Nishina regimes. Photoabsorption by interactions with internal jet radiation and the intergalactic background light (IBL) is included. Doppler factors, magnetic fields, and absolute jet powers are obtained by fitting the {\em HESS} and {\em Swift} data of the recent giant TeV flare observed from \object{PKS 2155--304}. For the contemporaneous {\em Swift} and {\em HESS} data from 28 and 30 July 2006, respectively, Doppler factors $\gtrsim 60$ and absolute jet powers $\gtrsim 10^{46}$ ergs s$^{-1}$ are required for a synchrotron/SSC model to give a good fit to the data, for a low intensity of the IBL and a ratio of 10 times more energy in hadrons than nonthermal electrons. Fits are also made to a TeV flare observed in 2001 from Mkn 421 which require Doppler factors $\gtrsim 30$ and jet powers $\gtrsim 10^{45}$ erg s$^{-1}$.