<i>FERMI</i> LARGE AREA TELESCOPE SECOND SOURCE CATALOG

TLDR

The 2FGL analysis uses improved diffuse Galactic and isotropic models, yet 162 sources receive caution flags due to possible confusion with residual imperfections. The paper presents the second Fermi‑LAT catalog of high‑energy gamma‑ray sources and compares it with the first catalog. Sources were detected using average 24‑month fluxes, with positions, spectra, five‑band fluxes, and monthly light curves provided for each entry. The catalog lists 1,873 sources, including 127 firmly identified and 1,170 reliably associated, with twelve sources modeled as spatially extended.

Abstract

We present the second catalog of high-energy gamma-ray sources detected by the Large Area Telescope (LAT), the primary science instrument on the Fermi Gamma-ray Space Telescope (Fermi), derived from data taken during the first 24 months of the science phase of the mission, which began on 2008 August 4. Source detection is based on the average flux over the 24-month period. The Second Fermi-LAT catalog (2FGL) includes source location regions, defined in terms of elliptical fits to the 95% confidence regions and spectral fits in terms of power-law, exponentially cutoff power-law, or log-normal forms. Also included are flux measurements in 5 energy bands and light curves on monthly intervals for each source. Twelve sources in the catalog are modeled as spatially extended. We provide a detailed comparison of the results from this catalog with those from the first Fermi-LAT catalog (1FGL). Although the diffuse Galactic and isotropic models used in the 2FGL analysis are improved compared to the 1FGL catalog, we attach caution flags to 162 of the sources to indicate possible confusion with residual imperfections in the diffuse model. The 2FGL catalog contains 1873 sources detected and characterized in the 100 MeV to 100 GeV range of which we consider 127 as being firmly identified and 1170 as being reliably associated with counterparts of known or likely gamma-ray-producing source classes.