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Resolving the Extragalactic γ-Ray Background above 50 GeV with the Fermi Large Area Telescope.

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Summary
This summary is machine-generated.

The Fermi Large Area Telescope (LAT) catalog reveals extragalactic gamma-ray sources are consistent with a Euclidean distribution. Blazars likely dominate these high-energy sources, accounting for most of the extragalactic gamma-ray background.

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Area of Science:

  • High-energy astrophysics
  • Gamma-ray astronomy
  • Cosmic ray physics

Background:

  • The Fermi Large Area Telescope (LAT) catalog (2FHL) provides 360 sources detected above 50 GeV.
  • Pass 8 data reprocessing significantly improved instrument performance.
  • Most high-Galactic latitude 2FHL sources are blazars.

Purpose of the Study:

  • To determine the source count distribution (dN/dS) of extragalactic gamma-ray sources above 50 GeV.
  • To constrain the dN/dS below the detection threshold.
  • To estimate the contribution of point sources to the extragalactic gamma-ray background.

Main Methods:

  • Detailed Monte Carlo simulations to measure dN/dS.
  • One-point photon fluctuation analysis to probe flux below the detection threshold.
  • Analysis of the 2FHL catalog derived from 80 months of Fermi-LAT data.

Main Results:

  • The source count distribution is compatible with a Euclidean distribution down to ~8x10^-12 ph cm^-2 s^-1.
  • The dN/dS is consistent with a broken power law, with a break flux between 8x10^-12 and 1.5x10^-11 ph cm^-2 s^-1.
  • Point sources constitute at least 86% of the extragalactic gamma-ray background.

Conclusions:

  • The observed dN/dS suggests a single population, likely blazars, dominates the extragalactic gamma-ray source population down to the lowest fluxes.
  • The findings provide crucial input for estimating source densities for future instruments like the Cherenkov Telescope Array.