What can be learnt from UHECR anisotropies observations. I. Large-scale anisotropies and composition features

Vol. 664
4. Extragalactic astronomy

What can be learnt from UHECR anisotropies observations. I. Large-scale anisotropies and composition features

The origin of a possible anisotropy in the arrival distribution of ultra-high-energy cosmic rays has been the subject of intense debate for nearly a decade. This paper presents the study of the most comprehensive modeling effort to date to examine the implications of different models on the robustness of the claimed origins. With a generic yet physically motivated source spectrum for the catalog galaxies, the propagation was modeled using a turbulent intergalactic magnetic field with a Kolmogorov spectrum and a scale length of 200 kpc. Several independent models were included for the global Galactic magnetic field constrained by the Planck synchrotron emission. A clever back-propagation model was employed to connect local measurements to the extragalactic incident particles. The detector energy resolution and reconstruction characteristics were also included. The resulting suite of simulations shows that source identifications are still consistent with chance and that the amplitude dipole distribution observed by Auger is a generic outcome of the simulations, but the orientation is not.