A closer look at the spectrum and small scale anisotropies of ultrahigh energy cosmic rays

We present results of numerical simulations of the propagation of ultrahigh energy cosmic rays (UHECRs) over cosmological distances, aiming at quantifying the statistical significance of the highest energy data on the spectrum and small scale anisotropies as detected by the AGASA experiment. We assess the significance of the lack of a GZK feature and its compatibility with the reported small scale anisotropies. Assuming that UHECRs are protons from extragalactic sources, we find that spectra with shape similar to that observed by AGASA can arise due to low statistics of detected events with a probability of 6 x 10(-4) for a continuous source distribution. However, when the spectrum is combined with the information on the small scale anisotropies reported by AGASA, the probability of getting both at the same time becomes as low as 2 x 10(-5). Our analysis of the AGASA results shows the power that will derive combining spectrum and small scale anisotropy data in future high statistics experiments, such as Auger ones.