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Paper: Broadband Properties of Candidate Blazar Counterparts of Unidentified EGRET Sources
Volume: 350, Blazar Variability Workshop II: Entering the GLAST Era
Page: 128
Authors: Bloom, S.D.
Abstract: The nature of most unidentified EGRET sources remains a mystery; however, a significant percentage of those out of the Galactic plane are likely to be blazars, if they are just weaker cousins of the known EGRET blazars. Blazar spectra are broad band in nature, and are characterized by two broad peaks in their spectral energy distributions (SED), one at low frequencies dominated by synchrotron emission, and the other up to GeV (or even TeV) gamma-ray energies dominated by upscattered radiation. All blazars, are thought to fit into a continuum of spectral shapes from fairly evenly distributed power to those that are dominated by the high energy spectrum. We hypothesize that candidate EGRET blazars (proposed counterparts to unidentified sources) should also fit into this scheme. By using broad band spectral indicies we can characterize the SEDs in a similar manner to that applied to the blazars in general that have better determined SEDs. We determine that the range of αro, a broad band spectral index that measures the location of the low energy peak, is somewhat more skewed to higher values than those of gamma-ray blazars, possibly indicating systematically lower synchroton peak frequencies of the SED. The spectral index, αog has a narrower range than that of blazars, and does not include the largest values, indicating that as a group, these candidate sources have more greatly gamma-ray dominated spectra than the blazars. Thus, if this collection of sources is mostly blazars, it is significantly less heterogeneous than the accepted group of well identified gamma-ray blazars. We do not find strong correlations between radio luminosity, gamma-ray luminosity or spectral shape that remain after the effects of redshift are removed. We also can not discern between the synchrotron self-Compton (SSC) or extenal Compton (EC) processes as being responsible for the gamma rays with these limited data.
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