Synchrotron Self-Compton Analysis of TeV X-ray Selected BL Lacertae Objects (0802.1529v2)

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$^{-1}$.

• The paper introduces an SSC framework to analyze multiwavelength data from XBLs, reducing model complexity by leveraging variability timescales and Doppler factors.
• It shows that TeV flares from PKS 2155–304 and Mkn 421 require high Doppler factors (>60 and >30) with jet powers exceeding 10^46 and 10^45 erg/s respectively.
• The findings offer actionable insights into particle acceleration processes and the potential roles of both leptonic and hadronic emission models in blazar jets.

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

This paper proposes a methodological framework for the analysis of multiwavelength observational data from X-ray-selected BL Lacertae (XBL) objects, specifically focusing on their detection in the TeV energy regime. The authors approach this analysis by applying a synchrotron self-Compton (SSC) model, which assumes the nonthermal synchrotron emission from electrons in relativistic jets of blazars, and uses this to compute the SSC spectrum based on key parameters such as the Doppler factor, magnetic field, and variability timescale. The variability timescale, a characteristic that indicates rapid changes in emission levels, is leveraged to infer the comoving blob radius using light-travel time arguments, reducing the complexity of the system to two essential parameters.

The detailed fitting to observed data, notably the giant TeV flare from PKS 2155–304, as observed by HESS and Swift in July 2006, reveals critical insights into the Doppler factors and the underlying jet dynamics. These observations require Doppler factors exceeding 60 and suggest absolute jet powers greater than $10^{46}$ ergs per second, assuming low levels of intergalactic background light (IBL) and a significant energy component in hadrons versus nonthermal electrons.

When applied to the 2001 flare of Mkn 421, this methodology stipulates Doppler factors greater than 30 and jet powers exceeding $10^{45}$ erg/s, situating these findings within the context of both theoretical constraints and practical implications for modeling blazar emission mechanisms.

The analysis addresses two principal potential models for the generation of such high-energy emission: leptonic models, such as the SSC process discussed, and hadronic models, which ascribe high-energy emissions to interactions involving protons. The paper further situates these findings relative to constraints imposed by the observed rapid variability at X-ray and $\gamma$-ray energies, postulating significant implications for particle acceleration processes within blazar jets, and acknowledges the challenges posed by the often-superluminal motions observed in blazar emissions.

In terms of future research directions, the paper implicitly suggests that extending the analysis to include potential contributions from undetected or unmodeled external photon fields could be critical. Additionally, the paper highlights the opportunity for instruments such as the Fermi Gamma-ray Space Telescope to validate these models through observations of correlated variability across different energy bands.

In conclusion, the work presented is a technical deep dive into modeling blazar emissions, providing a refined approach to understanding and predicting the behavior of these enigmatic astrophysical sources. The results offer a robust framework for examining and potentially reconciling diverse observational phenomena associated with XBLs and other high-energy astrophysical processes.