Blazar Gamma-Rays, Shock Acceleration, and the Extragalactic Background Light

TL;DR

This paper explores how shock acceleration in blazar jets influences gamma-ray spectra, affecting the use of blazars as probes for the extragalactic background light and suggesting correlations between spectral flatness, luminosity, and redshift.

Contribution

It demonstrates that relativistic shock acceleration can produce gamma-ray spectra with indices less than 1.5, altering previous constraints on the extragalactic infrared background and revealing potential spectral-luminosity-redshift correlations.

Findings

Relativistic shocks can produce gamma-ray spectra with indices below 1.5.

Flatter TeV spectra are associated with higher intrinsic luminosities.

Possible correlation between spectral flatness, luminosity, and redshift.

Abstract

The observed spectra of blazars, their intrinsic emission, and the underlying populations of radiating particles are intimately related. The use of these sources as probes of the extragalactic infrared background, a prospect propelled by recent advances in TeV-band telescopes, soon to be augmented by observations by NASA's upcoming Gamma-Ray Large Area Space Telescope (GLAST), has been a topic of great recent interest. Here, it is demonstrated that if particles in blazar jets are accelerated at relativistic shocks, then gamma-ray spectra with indices less than 1.5 can be produced. This, in turn, loosens the upper limits on the near infrared extragalactic background radiation previously proposed. We also show evidence hinting that TeV blazars with flatter spectra have higher intrinsic TeV gamma-ray luminosities and we indicate that there may be a correlation of flatness and luminosity with redshift.