Statistical Measurement of the Gamma-ray Source-count Distribution as a Function of Energy

Abstract

Photon counts statistics have recently been proven to provide a sensitive observable for characterizing gamma-ray source populations and for measuring the composition of the gamma-ray sky. In this work, we generalize the use of the standard 1-point probability distribution function (1pPDF) to decompose the high-latitude gamma-ray emission observed with Fermi-LAT into: (i) point-source contributions, (ii) the Galactic foreground contribution, and (iii) a diffuse isotropic background contribution. We analyze gamma-ray data in five adjacent energy bands between 1 and 171 GeV. We measure the source-count distribution dN/dS as a function of energy, and demonstrate that our results extend current measurements from source catalogs to the regime of so far undetected sources. Our method improves the sensitivity for resolving point-source populations by about one order of magnitude in flux. The dN/dS distribution as a function of flux is found to be compatible with a broken power law. We derive upper limits on further possible breaks as well as the angular power of unresolved sources. We discuss the composition of the gamma-ray sky and capabilities of the 1pPDF method.

arXiv comment4 pages, 2 figures. Proceedings, 6th International Symposium on High-Energy Gamma-Ray Astronomy (Gamma2016), Heidelberg, Germany, July 11-15, 2016

References in corpus (8)

• The spectrum of isotropic diffuse gamma-ray emission between 100 MeV and 820 GeV
• The Fermi Large Area Telescope On Orbit: Event Classification, Instrument Response Functions, and Calibration
• Evidence for Unresolved Gamma-Ray Point Sources in the Inner Galaxy
• The nature of the Diffuse Gamma-Ray Background
• Statistics of gamma-ray point sources below the Fermi detection limit
• The Denoised, Deconvolved, and Decomposed Fermi $\gamma$-ray sky - An application of the D${}^3$PO algorithm
• Unveiling the Gamma-ray Source Count Distribution Below the Fermi Detection Limit with Photon Statistics
• Statistical Measurement of the Gamma-ray Source-count Distribution as a Function of Energy

Cited by in corpus (1)

• Characterizing the Expected Behavior of Non-Poissonian Template Fitting