Search for a mass dependent anisotropy of UHECRs with the Pierre Auger Observatory

The origin of cosmic rays (CRs) is an open and exciting topic in astrophysics. On this theme, the Pierre Auger Observatory investigates the anisotropies of the ultra-high-energy cosmic rays (UHECRs) — which possess energies above ∼1 EeV — at small, intermediate, and large angular scales. The Observatory (with the surface detector stations spread over 3000 km2) has been collecting data for nearly 20 years, reaching more than 135 000 km2 yr sr of accumulated exposure. So far, one of the most significant discoveries is a large-scale dipole structure with an amplitude of ∼7%. This results from a modulation in right ascension for events with energies above 8 EeV, where the dipole equatorial component has a statistical significance of over 5σ. The source of this structure is not yet understood. It could arise from diffusion and deflection of CRs in magnetic fields, and/or could be caused by the anisotropic distribution of nearby sources. In either case, a dependence on the charge and/or mass of the CRs is expected on both the amplitude and direction of the observed dipole. For the first time, the Auger Observatory is preparing to include information on the UHECR composition in a search for a mass-dependence signature on the observed dipole. ... mehrIn this contribution, we discuss the prospects of anisotropy searches in light of mass-composition information of Phase 1 of the Pierre Auger Observatory.