http://arxiv.org/abs/1711.03111
The Fermi Large Area Telescope (LAT) Collaboration has recently released the Third Catalog of Hard Fermi-LAT Sources (3FHL), which contains 1556 sources detected above 10 GeV with seven years of Pass 8 data. We investigate the source count distribution of 3FHL sources at Galactic latitudes $|b|>20^{\circ}$, where the sources are mostly blazars. We use two complementary techniques: 1) a source-detection efficiency correction method and 2) an analysis of pixel photon count statistics with the 1-point probability distribution function (1pPDF). With the first method, using realistic Monte Carlo simulations of the $\gamma$-ray sky, we calculate the efficiency of the LAT to detect point sources. This enables us to find the intrinsic source count distribution at photon fluxes down to $7.5\times10^{-12}$ ph cm$^{-2}$s$^{-1}$. With this method we detect a flux break at $(3.5\pm0.4) \times 10^{-11} \mathrm{ph}\,\mathrm{cm}^{-2}\mathrm{s}^{-1}$ with a significance of at least $5.4 \sigma$. The power-law indexes of the source count distribution above and below the break are $2.09\pm0.04$ and $1.07\pm0.27$, respectively. This result is confirmed with the 1pPDF method, which has a sensitivity reach of $\sim10^{-11}$ ph cm$^{-2}$s$^{-1}$. Integrating the derived source count distribution above the sensitivity of our analysis, we find that $(42\pm8)\%$ of the extragalactic $\gamma$-ray background originates from blazars.
M. Mauro, S. Manconi, H. Zechlin, et. al.
Fri, 10 Nov 17
33/55
Comments: 12 pages, 13 figures, 3 table. Submitted to ApJ