The Redshift Dependence of Gamma-Ray Absorption in the Environments of Strong-Line AGNs
Abstract
The case of γ-ray absorption due to photon-photon pair production of jet photons in the external photon environments, such as the accretion disk and the broad-line region radiation fields, of γ-ray-loud active galactic nuclei (AGNs) that exhibit strong emission lines is considered. I demonstrate that this ``local opacity,'' if detected, will almost unavoidably be redshift-dependent in the sub-TeV range. This introduces nonnegligible biases and complicates approaches for studying the evolution of the extragalactic background light with contemporary GeV instruments such as the Gamma-Ray Large Area Space Telescope (GLAST), where the γ-ray horizon is probed by means of statistical analysis of absorption features (e.g., the Fazio-Stecker relation) in AGN spectra at various redshifts. It particularly applies to strong-line quasars, where external photon fields are potentially involved in γ-ray production.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- August 2007
- DOI:
- 10.1086/519766
- arXiv:
- arXiv:0705.1534
- Bibcode:
- 2007ApJ...665.1023R
- Keywords:
-
- Cosmology: Diffuse Radiation;
- Galaxies: Active;
- Galaxies: Evolution;
- Galaxies: Nuclei;
- Gamma Rays: Theory;
- Radiation Mechanisms: Nonthermal;
- Astrophysics
- E-Print:
- 19 pages, 5 figures