Ultrahigh energy nuclei propagation in a structured, magnetized universe

Abstract

We compare the propagation of iron and proton nuclei above 10 19 eV in a structured Universe with source and magnetic field distributions obtained from a large scale structure simulation and source densities ∼ 10 −5 Mpc −3 . All relevant cosmic ray interactions are taken into account, including photo-disintegration and propagation of secondary products. Iron injection predicts spectral shapes different from proton injection which disagree with existing data below ≃ 30 EeV. Injection of light nuclei or protons must therefore contribute at these energies. However, at higher energies, existing data are consistent with injection of pure iron with spectral indices between ∼ 2 and ∼ 2.4. This allows a significant recovery of the spectrum above ≃ 100 EeV, especially in the case of large deflections. Significant auto-correlation and anisotropy, and considerable cosmic variance are also predicted in this energy range. The mean atomic mass A fluctuates considerably between different scenarios. At energies below 60 EeV, if the observed A > ∼ 35, magnetic fields must have a negligible effect on propagation. At the highest energies the observed flux will be dominated by only a few sources whose location may be determined by next generation experiments to within 10 − 20 • even if extra-galactic magnetic fields are important.

Cosmogenic gamma rays and the composition of cosmic rays

“…Right panel: The corresponding spectra of cosmogenic γ-rays (dashed lines) and neutrinos (dotted line) for the two models. The diffuse γ-ray spectrum of the proton model is marginally consistent with the diffuse extra-galactic spectrum inferred by Fermi-LAT [51] and the diffuse upper limit on cosmogenic neutrinos from the 40-string configuration (IC40) of IceCube [55]. The cosmogenic γ-ray and neutrino spectra of the iron model are two orders of magnitude below the proton model predictions.…”

“…This possibility has been previously studied for proton sources in Refs. [51][52][53][54] and has been revived recently in the context of unusually bright though distant TeV γ-ray sources [55][56][57]. Here we extend the discussion to the case of UHE CR nuclei and study the effect of IGMFs on the observability of the PS flux in detail.…”

Extragalactic propagation of ultrahigh energy cosmic-rays

“…More recently, Khan et al [38], proposed new estimates of the GDR cross section, based on theoretical calculation using the TALYS nuclear reaction code [39,40], showing a better agreement with the available data than previous parametrizations from [32]. In recent years the interest in the propagation of UHECR nuclei has significantly grown [41,42,43,44,45,46,47,48,49]. This is all the more true since the recent composition analyses of the Pierre Auger Observatory seem to indicate a possible significant contribution of nuclei at the highest energies [10].…”

“…We will also not discuss in detail the impact of extragalactic magnetic fields on the expected anisotropies of the UHECR sky. Detailed discussions (including for some of them a discussion on composition or a proposed interpretation of the available data) can be found, for instance, in [118,119,120,42,121,122,123,124,125] and compared with the case of negligible fields studied in [126].…”

Propagation of ultrahigh energy cosmic rays in extragalactic magnetic fields: a view from cosmological simulations

“…However, such a simulation is very inefficient as only very few events reach the observer, and the computation is dominated by the propagation of particles that do not reach the observer (Armengaud et al 2005). On the other hand, a finite size of the observer can introduce spurious effects in the measurements of the anisotropy of UHECRs, and must be treated with care (see below).…”