Diffuse flux of ultra-high energy photons from cosmic-ray interactions in the disk of the Galaxy and implications for the search for decaying super-heavy dark matter

Abstract

An estimate of the expected photon flux above $10^{17}$eV from the interactions of ultra-high energy cosmic rays with the matter in the Galactic disk is presented. Uncertainties arising from the distribution of the gas in the disk, the absolute level of the cosmic ray flux, and the composition of the cosmic rays are taken into account. Within these uncertainties, the integrated photon flux above $10^{17}$eV is, averaged out over Galactic latitude less than $5^{\circ }$, between $\simeq 3.2\times 10^{-2}$km${}^{-2}$yr${}^{-1}$sr${}^{-1}$ and $\simeq 8.7\times 10^{-2}$km${}^{-2}$yr${}^{-1}$sr${}^{-1}$. The all-sky average value amounts to $\simeq 1.1\times 10^{-2}$km${}^{-2}$yr${}^{-1}$sr${}^{-1}$ above $10^{17}$eV and decreases roughly as $E^{-2}$, making this diffuse flux the dominant one from cosmic-ray interactions for energy thresholds between $10^{17}$eV and $10^{18}$~eV. Compared to the current sensitivities of detection techniques, a gain between two and three orders of magnitude in exposure is required for a detection below $\simeq 10^{18}$~eV. The implications for searches for photon fluxes from the Galactic center that would be indicative of the decay of super-heavy dark matter particles are discussed, as the photon flux presented in this study can be considered as a floor below which other signals would be overwhelmed.

accepted for publication in ApJ

References in corpus (10)

• First Detection of sub-PeV Diffuse Gamma Rays from the Galactic Disk: Evidence for Ubiquitous Galactic Cosmic Rays beyond PeV Energies
• Features of the energy spectrum of cosmic rays above $2.5\times 10^{18}$ eV using the Pierre Auger Observatory
• Gravitational Production of Dark Matter during Reheating
• The Five College Radio Astronomy Observatory CO Mapping Survey of the Taurus Molecular Cloud
• The energy spectrum of cosmic rays beyond the turn-down around $10^{17}$ eV as measured with the surface detector of the Pierre Auger Observatory
• Radiative Production of Non-thermal Dark Matter
• KASCADE-Grande Limits on the Isotropic Diffuse Gamma-Ray Flux between 100 TeV and 1 EeV
• The primary cosmic-ray energy spectrum measured with the Tunka-133 array
• Hunting for super-heavy dark matter with the highest-energy cosmic rays
• Diffuse flux of galactic neutrinos and gamma rays

Cited by in corpus (7)

• A search for photons with energies above $2\times 10^{17}$ eV using hybrid data from the low-energy extensions of the Pierre Auger Observatory
• Limits on the cosmic neutrino background
• Revisiting ultrahigh-energy constraints on decaying super-heavy dark matter
• Searches for Ultra-High-Energy Photons at the Pierre Auger Observatory
• Search for a diffuse flux of photons with energies above tens of PeV at the Pierre Auger Observatory
• Constraints on metastable superheavy dark matter coupled to sterile neutrinos with the Pierre Auger Observatory
• Constraints on superheavy dark matter decaying into $h\nu$, $Z\nu$ and $W\ell$ -- Benchmark example within an extended seesaw framework