3FHL: The Third Catalog of Hard Fermi-LAT Sources

Abstract

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), containing 1556 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 associated with extragalactic counterparts at other wavelengths, including 16 sources located at very high redshift (z > 2). Of the sources, 8% have Galactic counterparts and 13% are unassociated (or associated with a source of unknown nature). The high-latitude sky and the Galactic plane are observed with a flux sensitivity of 4.4 to 9.5×10 −11 phcm −2 s −1 , respectively (this is approximately 0.5% and 1% of the Crab Nebula flux above 10 GeV). The catalog includes 214 new γ-ray sources. The substantial increase in the number of photons (more than 4 times relative to 1FHL and 10 times to 2FHL) also allows us to measure significant spectral curvature for 32 sources and find flux variability for 163 of them. Furthermore, we estimate that for the same 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, highlighting the importance, for future Cherenkov telescopes, of lowering the energy threshold as much as possible.

Unidentified gamma-ray sources as targets for indirect dark matter detection with theFermi-Large Area Telescope

“…This rate of false positives is expected to be under 5% according to the Bayesian analysis in the considered catalogs, although this number can be significantly smaller, e.g. a 1% in the 3FHL [18].…”

“…The Fermi-LAT is a pair conversion telescope designed to observe the energy band from 20 MeV to greater than 300 GeV. Several point-source Fermi-LAT catalogs have been released and contain hundreds to thousands of gamma-ray objects, many of them previously unknown [16][17][18]. The various catalogs cover different energy ranges and exposure times, and each was constructed with the best available astrophysical diffuse emission model and instrumental response functions (IRFs).Many groups have used Fermi-LAT data to constrain the WIMP DM parameter space: for example through observations of the diffuse extragalactic emission [19], galaxy clusters [20], gamma-ray lines [21,22] and the previously mentioned dSphs [23], or to claim possible detection of DM in the Galactic Center (GC) [24,25].…”

Optical Spectroscopic Survey of a Sample of Unidentified Fermi Objects

“…One object (3FGL J1129.0+3758) is found at z > 1.2, while four sources, with featureless spectra, are likely at z> 0.6. Fourteen out of 20 objects are detected by Fermi satellite at energies above 10 GeV (see the Third Catalog of Hard Fermi-LAT Sources (3FHL), Ajello et al 2017). Therefore, they are candidates to be good TeV targets for the Cherenkov telescopes.…”

Understanding the giant gamma-ray outburst on June 16, 2015 from the blazar 3C 279

“…We have analyzed high energy γ-ray data from the Fermi -LAT observations in the energy range 100 MeV -500 GeV using standard Fermitools (Fermi 1.0.1). The LAT is a pair-conversion telescope which directly detects γ-rays in the energy range from 20 MeV to more than 1 TeV (Atwood et al 2009;Ajello et al 2017). The publicly available Pass8 event data on blazar 3C 279 was downloaded from the Fermi -LAT data server 1 .…”