http://arxiv.org/abs/1710.05517
This work presents a scenario of ultra-high energy cosmic ray source distribution where a nearby source is solely responsible for the anisotropies in arrival directions of cosmic rays while the rest of the sources contribute only isotropically. An analytical approach focused on large-scale anisotropies, which are influenced by deflections in a Kolmogorov-type turbulent magnetic field, is employed to give more general results. When the recent Pierre Auger Observatory angular power spectrum above 8 EeV is used the model gives two solutions: weaker RMS deflections $\delta_\mathrm{rms}^+ = (95\pm 36)^\circ$ with the lower relative flux from the single source $\eta^+=0.38\pm 0.18$, or stronger RMS deflections $\delta_\mathrm{rms}^- = (113\pm 24)^\circ$ with the higher relative flux $\eta^-=0.49\pm 0.23$. It is shown that the first solution predicts a lower dipole amplitude at higher energies compared to the second solution. Furthermore, these solutions can be translated into constraints on the source distance, luminosity, and extragalactic magnetic field strength. For Centaurus A and Virgo cluster the required relation between the coherence length and the RMS magnetic field strength is obtained: a coherence length of $~\sim 10\,\mathrm{kpc}$ would imply RMS field strengths above $1\,\mathrm{nG}$ for iron dominated and above $10\,\mathrm{nG}$ for proton dominated composition. A comparison of the model with advanced Monte Carlo techniques is performed to show its applicability in a realistic, structured magnetic field and to analyze structured field effects on the anisotropies. The result of the comparison shows a tendency of structured fields to suppress large scale anisotropies, especially the dipole, compared to those anisotropies of smaller scales.
A. Dundovic and G. Sigl
Tue, 17 Oct 17
24/163
Comments: 22 pages, 11 figures