Special Universe Talk: Cosmogenic neutrinos and gamma-rays constrain UHECR source models

by Arjen van Vliet (Radboud Universiteit, NL)

Friday, 19 May 2017 from to (Europe/Berlin)
at Universe Cluster, Boltzmannstr. 2, Garching ( seminar room, basement )
! Start time changed from 11am to 10am!

Abstract: 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. We developed a public astrophysical simulation framework for propagating extraterrestrial ultra-high energy particles, CRPropa 3, which is ideally suited for predicting the level of these fluxes. CRPropa includes all relevant UHECR interactions as well as secondary neutrino and electromagnetic cascade production and propagation. Our results show that 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. Pure-proton models with a source evolution corresponding to possible UHECR sources are already strongly constrained by both the neutrino flux measured by IceCube and the extragalactic gamma-ray background measured by Fermi/LAT. On the other hand a model optimised to provide the best fit to the UHECR spectrum and composition measured by the Pierre Auger Collaboration gives significantly less cosmogenic neutrinos and gamma-rays. With a few more years of data neutrino and gamma-ray measurements might be able to rule out all realistic pure-proton models. Furthermore, future neutrino experiments with sensitivities of ~10-8–10-10 GeV cm-2 s-1 sr-1 in the EeV range will be able to constrain the fraction of protons present in UHECRs.