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A one-year-long simulation of the ~300 blazars expected to be the brightest in the gamma-ray sky as seen by GLAST
was performed. The simulation included galactic and extragalactic gamma-ray backgrounds and a detailed model for the variability and spectrum of such blazars. To simulate the EBL attenuation we use the "Best Fit" model from Kneiske et al [9].
Figure 3 presents a scatter plot of the energy cutoff vs redshift obtained from the analysis of the Monte Carlo simulation. This relation was first introduced by Fazio & Stecker in 1970 10 as a way to relate the energy
cutoff with the redshift of the source. Kneiske et al 9 have proposed to use the Fazio-Stecker relation (FSR) to
compare EBL models with the FSR distribution obtained from observations. This idea is implemented here by considering the FSR obtained after determination of the cutoff energies of the brightest blazars expected to be observed with GLAST. In the absence of blazar intrinsic absorption and strong blazar spectrum curvature, the data points in the FSR plot will converge (amid statistical fluctuations) to the true curve due to EBL absorption. If it turns out, however, that this is not the case for a few or most blazars, their measured cut-off energies would spread below the EBL-induced value, but never above. This would enable at least and upper limit on EBL attenuation (least-attenuated flux in a particular redshift range).
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