Implications of gamma-ray observations on proton models of UHECR

Abstract

The origin of ultra high energy cosmic rays (UHECR) is still unknown. However, great progress has been achieved in past years due to the good quality and large statistics in experimental data collected by the current observatories. The data of the Pierre Auger Observatory show that the composition of the UHECRs becomes progressively lighter starting from $10^{17}$ eV up to $\sim 10^{18.3}$ eV and then, beyond that energy, it becomes increasingly heavier. These analyses are subject to important systematic uncertainties due to the use of hadronic interaction models that extrapolate lower energy accelerator data to the highest energies. Although proton models of UHECRs are disfavored by these results, they cannot be completely ruled out. It is well known that the energy spectra of gamma rays and neutrinos, produced during propagation of these very energetic particles through the intergalactic medium, are a useful tool to constrain the spectrum models. In particular, it has recently been shown that the neutrino upper limits obtained by IceCube challenge the proton models at 95% CL. In this work we study the constraints imposed by the extragalactic gamma-ray background, measured by Fermi-LAT, on proton models of UHECRs. In particular, we make use of the extragalactic gamma-ray background flux, integrated from 50 GeV to 2 TeV, that originates in point sources, which has recently been obtained by the Fermi-LAT collaboration, in combination with the neutrino upper limits, to constrain the emission of UHECRs at high redshits ($z>1$), in the context of the proton models.

References in corpus (9)

• The spectrum of isotropic diffuse gamma-ray emission between 100 MeV and 820 GeV
• Depth of Maximum of Air-Shower Profiles at the Pierre Auger Observatory: Measurements at Energies above 10^17.8 eV
• GZK Neutrinos after the Fermi-LAT Diffuse Photon Flux Measurement
• Study of Ultra-High Energy Cosmic Ray Composition Using Telescope Array's Middle Drum Detector and Surface Array in Hybrid Mode
• A dip in the UHECR spectrum and the transition from galactic to extragalactic cosmic rays
• Constraints on the origin of cosmic rays above $10^{18}$ eV from large scale anisotropy searches in data of the Pierre Auger Observatory
• Signatures of the transition from galactic to extragalactic cosmic rays
• Cosmogenic photons as a test of ultra-high energy cosmic ray composition
• Diffusion of Cosmic Rays in the Expanding Universe. II. Energy Spectra of Ultra-High Energy Cosmic Rays

Cited by in corpus (4)

• Ultra-High-Energy Cosmic Rays: The Intersection of the Cosmic and Energy Frontiers
• Secondary neutrino and gamma-ray fluxes from SimProp and CRPropa
• Ultra High Energy Cosmic Ray Source Models: Successes, Challenges and General Predictions
• Implications of gamma-ray and neutrino observations on source models of ultrahigh energy cosmic rays