The Effect of Blazar Spectral Breaks on the Blazar Contribution to the Extragalactic Gamma-ray Background

Abstract

The spectral shapes of the contributions of different classes of unresolved gamma-ray emitters can provide insight into their relative contributions to the extragalactic gamma-ray background (EGB) and the natures of their spectra at GeV energies. We calculate the spectral shapes of the contributions to the EGB arising from BL Lacertae type objects (BL Lacs) and flat-spectrum radio quasars (FSRQs) assuming blazar spectra can be described as broken power laws. We fit the resulting total blazar spectral shape to the Fermi Large Area Telescope measurements of the EGB, finding that the best-fit shape reproduces well the shape of the Fermi EGB for various break scenarios. We conclude that a scenario in which the contribution of blazars is dominant cannot be excluded on spectral grounds alone, even if spectral breaks are shown to be common among Fermi blazars. We also find that while the observation of a featureless (within uncertainties) power-law EGB spectrum by Fermi does not necessarily imply a single class of contributing unresolved sources with featureless individual spectra, such an observation and the collective spectra of the separate contributing populations determine the ratios of their contributions. As such, a comparison with studies including blazar gamma-ray luminosity functions could have profound implications for the blazar contribution to the EGB, blazar evolution, and blazar gamma-ray spectra and emission.

8 pages, emulateapj format; 5 figures; accepted for publication in ApJ

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• The Second Catalog of Active Galactic Nuclei Detected by the Fermi Large Area Telescope
• On The Gamma-Ray Emission From Reticulum II and Other Dwarf Galaxies
• The Extragalactic Gamma-ray Sky in the Fermi era
• The Star-Forming Galaxy Contribution to the Cosmic MeV and GeV Gamma-Ray Background
• The Contribution of Blazars to the Extragalactic Diffuse Gamma-ray Background and Their Future Spatial Resolution
• Flux and Photon Spectral Index Distributions of Fermi-LAT Blazars And Contribution To The Extragalactic Gamma-ray Background
• Current and Future Constraints on Dark Matter from Prompt and Inverse-Compton Photon Emission in the Isotropic Diffuse Gamma-ray Background
• Constraints on Dark Matter Annihilation/Decay from the Isotropic Gamma-Ray Background
• Improving the Sensitivity of Gamma-Ray Telescopes to Dark Matter Annihilation in Dwarf Spheroidal Galaxies
• Probing the Intergalactic Magnetic Field with the Anisotropy of the Extragalactic Gamma-ray Background
• A Determination of the Gamma-ray Flux and Photon Spectral Index Distributions of Blazars from the Fermi-LAT 3LAC
• Novel Techniques for Decomposing Diffuse Backgrounds
• The contribution from blazar cascade emission to the extragalactic gamma-ray background: What a role does the extragalactic magnetic field play?
• The Diffuse Gamma-ray Background from Type Ia Supernovae
• Analysis of Fermi-LAT data from Tucana-II: Possible constraints on the Dark Matter models with an intriguing hint of a signal