MULTIWAVELENGTH PROBES OF THE ENVIRONS OF RELATIVISTIC SHOCKS IN BLAZAR JETS

Matthew G Baring,Errol J Summerlin,M Böttcher

doi:10.1142/s2010194514601677

Abstract

Diffusive shock acceleration (DSA) at relativistic shocks is likely to be an important acceleration mechanism in various astrophysical jet sources, including radio-loud AGN. An important recent development for blazar science is the ability of Fermi-LAT data to pin down the power-law index of the high energy portion of emission in these sources, and therefore also the index of the underlying non-thermal particle population. This diagnostic potential was not possible prior to Fermi launch, when gamma-ray information was dominated by the highly-absorbed TeV band. This paper highlights how multiwavelength spectra including X-ray band and Fermi data can be used to probe diffusive acceleration in relativistic, oblique, MHD shocks in blazar jets. The spectral index of the non-thermal particle distributions resulting from Monte Carlo simulations of DSA, and the fraction of thermal particles accelerated to non-thermal energies, depend sensitively on the particles' mean free path scale, and also on the magnetic field obliquity to the shock normal. We investigate self-consistently the radiative synchrotron/Compton signatures of the resulting thermal and non-thermal particle distributions. Important constraints on the frequency of particle scattering and the level of field turbulence are identified for the blazar AO 0235+164. The possible interpretation that turbulence levels decline with remoteness from jet shocks, and a significant role for non-gyroresonant diffusion, are discussed.

Highlights

Blazars are a class of active galaxies that are among the most powerful and dynamic extragalactic objects
By exploring a range of dependences of the diffusive mean free path λ on the momentum p of accelerated charges, the possible interpretation that turbulence levels decline with remoteness from a shock is identified, perhaps signalling a significant role for non-gyroresonant diffusion near blazar jet shocks
This paper has offered a detailed exploration of multi-wavelength spectral fits to flaring emission from the BL Lac object AO 0235+164 using electron distribution functions obtained directly from Monte Carlo simulations of diffusive acceleration at relativistic shocks

Summary

Introduction

Blazars are a class of active galaxies that are among the most powerful and dynamic extragalactic objects. The convective loss rates downstream of relativistic shocks are sensitive to the orientation of the mean magnetic field, and the character of the in situ MHD turbulence, yielding a wide variety of power-law indices for accelerated charges for a given velocity compression ratio.[15,16,17,18] gamma-ray spectroscopy of blazars can afford insights into details of the structure of shocks in jets It has been understood for nearly two decades[19] that diffusive shock acceleration is so efficient that low levels of field turbulence (spawning λ rg ) are required to accommodate synchrotron spectral peaks appearing in the X-ray band. By exploring a range of dependences of the diffusive mean free path λ on the momentum p of accelerated charges, the possible interpretation that turbulence levels decline with remoteness from a shock is identified, perhaps signalling a significant role for non-gyroresonant diffusion near blazar jet shocks

Shock Acceleration Simulations of Particle Distributions

Radiation Emission Modeling

Discussion

Conclusion