A global autocorrelation study after the first Auger data: impact on the number density of UHECR sources.

Abstract

We perform an autocorrelation study of the Auger data with the aim to constrain the number density ns of ultrahigh energy cosmic ray (UHECR) sources, estimating at the same time the effect on ns of the systematic energy scale uncertainty and of the distribution of UHECR. The use of global analysis has the advantage that no biases are introduced, either in ns or in the related error bar, by the a priori choice of a single angular scale. The case of continuous, uniformly distributed sources is nominally disfavored at 99% CL and the fit improves if the sources follow the large-scale structure of matter in the universe. The best-fit values obtained for the number density of proton sources are within a factor ~2 around ns 1 × 10–4Mpc–3 and depend mainly on the Auger energy calibration scale, with lower densities being preferred if the current scale is correct. The data show no significant small-scale clustering on scales smaller than a few degrees. This might be interpreted as a signature of magnetic smearing of comparable size, comparable with the indication of a 3° magnetic deflection coming from cross-correlation results. The effects of some approximations done on the above results are also discussed.