Effects of magnetic fields on anisotropies in a catalog based research

Ultra high energy cosmic rays (UHECRs) are charged particles which origins is still an open question in modern astrophysics. For the identification of valid sources, a key role is played by the Galactic magnetic field (GMF) which influences the arrival direction of charged particles.

Recent studies, by the Pierre Auger Collaboration, on the arrival direction of UHECRs showed the presence of anistropies above 40 EeV which indicates the contribution from nearby sources such as starburst galaxied (SBG) and active galactic nuclei (AGN). The likelihood analysis revealed a significance of 4.2σ for the starburst sample although the coherent deflections related to the GMF have not been considered.

In this work we focus our attention on the SBG catalog and we conduct the likelihood analysis on simulated datasets. The mock datasets are constructed by employing CRPropa3 for the extragalactic propagation and by adding an isotropic background. A lensing technique, considering the JF12 model for the GMF, is then applied to the simulated particles.

Our results show that the parameters as reported by the Pierre Auger Collaboration occur for 20% of all data sets. ... mehrHowever, due to the neglected coherent deflections, the inferred anisotropy fraction is a biased estimator and the true anisotropic fraction is always larger than the one derived from the likelihood fit.