Resolving the Extragalactic $\gamma$-ray Background above 50 GeV with Fermi-LAT

Understand

The Fermi Large Area Telescope (LAT) Collaboration has recently released a catalog of 360 sources detected above 50 GeV (2FHL).

• This catalog was obtained using 80 months of data re-processed with Pass 8, the newest event-level analysis, which significantly improves the acceptance and angular resolution of the instrument.
• Most of the 2FHL sources at high Galactic latitude are blazars.
• Using detailed Monte Carlo simulations, we measure, for the first time, the source count distribution, $dN/dS$, of extragalactic $\gamma$-ray sources at $E>50$ GeV and find that it is compatible with a Euclidean distribution down to the lowest measured source flux in the 2FHL ($\sim8\times 10^{-12}$ ph cm$^{-2}$ s$^{-1}$).