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

摘要

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