12-20 July 2017
Asia/Seoul timezone
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BEXCO - Room F(201/202/203/204)

[CRI221] Cosmogenic gamma-rays and neutrinos constrain UHECR source models


  • Arjen VAN VLIET

Primary authors



Purpose. When ultra-high-energy cosmic rays (UHECRs) travel through the universe they produce secondary neutrinos as well as photons, electrons and positrons (initiating electromagnetic cascades) in different kinds of interactions. These neutrinos and electromagnetic cascades are detected at Earth as isotropic extragalactic fluxes. The level of these fluxes can be directly predicted for any kind of UHECR model, providing the connection between cosmic ray, neutrino and gamma-ray measurements. Methods. We developed a public astrophysical simulation framework for propagating extraterrestrial ultra-high energy particles, CRPropa 3 (see crpropa.desy.de), which is ideally suited for this purpose. CRPropa includes all relevant UHECR interactions as well as secondary neutrino and electromagnetic cascade production and propagation. It is designed for high-performance computing and provides the flexibility to scan large parameter ranges of UHECR models. Results. The expected cosmogenic neutrino and gamma-ray spectra depend strongly on the evolution with redshift of the UHECR sources and on the chemical composition of UHECRs at injection. The dependence on the spectral index (assuming a power-law injection spectrum at the sources) and maximum acceleration energy is, on the other hand, relatively small. Pure proton models with a source evolution corresponding to possible UHECR sources (active galactic nuclei, gamma-ray bursts or sources following the star formation rate) are already strongly constrained by both the astrophysical neutrino flux measured by IceCube and the isotropic diffuse gamma-ray background measured by Fermi/LAT. On the other hand a model with the chemical composition, spectral index and maximum acceleration energy optimized to provide the best fit to the spectrum and composition measured by the Pierre Auger Collaboration gives significantly less cosmogenic neutrinos and gamma-rays. Conclusions. Neutrino and gamma-ray measurements are starting to constrain realistic UHECR models. With a few more years of data these measurements, combined with the UHECR spectrum, might be able to rule out all realistic pure-proton models.