# 3FHL: The Third Catalog of Hard Fermi-LAT Sources [HEAP]

We present a catalog of sources detected above 10 GeV by the Fermi-Large Area Telescope (LAT) in the first 7 years of data using the Pass 8 event-level analysis. This is the Third Catalog of Hard Fermi-LAT Sources (3FHL) and contains 1558 objects characterized in the 10 GeV–2 TeV energy range. The sensitivity and angular resolution are improved by factors of 3 and 2 relative to the previous LAT catalog at the same energies (1FHL). The vast majority of detected sources (79%) are extragalactic, including 16 sources located at very high redshift ($z>2$). Nine percent of the sources are Galactic and 12% are unassociated (or associated with a source of unknown nature). The high-latitude sky and the Galactic plane are observed with an average sensitivity of 0.5% and 1% of the Crab Nebula flux above 10 GeV, respectively. The catalog includes 225 new $\gamma$-ray sources. The substantial increase in the number of photons (more than 4 times relative to the 1FHL and 10 times to the 2FHL) also allows us to characterize spectral curvature for 32 sources and flux variability for 163 of them. Furthermore, we estimate that for the same energy flux limit of $10^{-12}$ erg cm$^{-2}$s$^{-1}$, the energy range above 10 GeV has twice as many sources as the range above 50 GeV, which confirms and quantifies the importance of lowering the energy threshold of Cherenkov telescopes as much as possible in order to increase the number of available sources.

Fermi-LAT Collaboration for the Fermi-LAT Collaboration et al.
Fri, 3 Feb 17
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Comments: Preliminary version. Contact authors: Alberto Dominguez, Marco Ajello, Benoit Lott, Sara Cutini, Pascal Fortin. The full FITS catalog will be made available at the FSSC: this https URL