Statistical measurement of the gamma-ray source-count distribution as a function of energy

Abstract

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.

IceCube neutrinos from hadronically powered gamma-ray galaxies

“…The remaining (non-blazar) fraction, is thought to be shared by all the other γ-ray emitters, such as normal and starburst galaxies and misaligned blazars. The share between the blazars and the non-blazar contribution varies between the different analyses, and are accompanied by large errors: the Fermi collaboration identifies the contribution from blazars to the EGB above 50 GeV as 86% +16 −14 % [41]; Lisanti et al [42] as 68% +9% −8% and Zechlin et al [43] as 81% +52% −19% . Complementary to this measurement, the contribution from HAGS to the extragalactic γ-ray background has been discussed in [ [44][45][46].…”

“…Here we show two different examples, assuming as a prototype source NGC 253 and ARP 220. In the last three columns on the right we write what is the tension between the contribution to the EGB expected from our model and the results of the three calculations discussed in the paper [41][42][43]. where dN dE is the differential flux at the source.…”

Constraining high-energy cosmic neutrino sources: Implications and prospects

“…yses [57,58,110,111] can be used for additional constraints, and the cross correlation gives stringent limits on contributions from star-forming galaxies including SBGs [112].…”

“…Finally, we note that a lower limit on the source density may be obtained from the upper limit on the anisotropy in the extragalactic gamma-ray background measured by Fermi (C p ≤ 2 × 10 −20 cm −4 s −2 sr −1 at 20 GeV [110], where C p is the angular power spectrum). The recent results obtained via the photon count fluctuation analyses [57,58,111,112] can be used for additional constraints, and the cross correlation gives stringent limits on contributions from star-forming galaxies including SBGs [113].…”