2FHL: The Second Catalog of Hard Fermi-LAT Sources

TL;DR

This paper presents the 2FHL catalog of 360 sources detected above 50 GeV by Fermi-LAT over 80 months, including spatially extended sources and improved localization, bridging the gap between space-based and ground-based gamma-ray observations.

Contribution

The paper introduces the second catalog of hard Fermi-LAT sources with enhanced detection and localization capabilities, including spatially extended sources, and highlights new potential targets for very high-energy follow-up.

Findings

Detected 360 sources above 50 GeV in 80 months.

86% of sources are associated with known counterparts, mostly active galactic nuclei.

Only 25% of sources are previously detected by Cherenkov telescopes.

Abstract

We present a catalog of sources detected above 50 GeV by the {\it Fermi}-Large Area Telescope (LAT) in 80 months of data. The newly delivered Pass 8 event-level analysis allows the detection and characterization of sources in the 50 GeV--2 TeV energy range. In this energy band, {\it Fermi}-LAT has detected 360 sources, which constitute the second catalog of hard {\it Fermi}-LAT sources (2FHL). The improved angular resolution enables the precise localization of point sources ($\sim$1.7$'$ radius at 68 % C.~L.) and the detection and characterization of spatially extended sources. We find that 86 % of the sources can be associated with counterparts at other wavelengths, of which the majority (75 %) are active galactic nuclei and the rest (11 %) are Galactic sources. Only 25 % of the 2FHL sources have been previously detected by Cherenkov telescopes, implying that the 2FHL provides a reservoir of candidates to be followed up at very high energies. This work closes the energy gap between the observations performed at GeV energies by {\it Fermi}-LAT on orbit and the observations performed at higher energies by Cherenkov telescopes from the ground.