Bounds on the density of sources of ultra-high energy cosmic rays from the Pierre Auger Observatory

TL;DR

This paper establishes lower bounds on the density of ultra-high energy cosmic ray sources based on the absence of clustering in their arrival directions, informing source distribution models.

Contribution

It provides new quantitative bounds on source densities of ultra-high energy cosmic rays using observational data from the Pierre Auger Observatory.

Findings

Source density > (0.06 - 5) x 10^-4 Mpc^-3 for uniform sources.

Source density > (0.2 - 7) x 10^-4 Mpc^-3 for sources following local matter.

Bounds depend on magnetic deflections.

Abstract

We derive lower bounds on the density of sources of ultra-high energy cosmic rays from the lack of significant clustering in the arrival directions of the highest energy events detected at the Pierre Auger Observatory. The density of uniformly distributed sources of equal intrinsic intensity was found to be larger than $\sim (0.06 - 5) \times 10^{-4}$ Mpc$^{-3}$ at 95% CL, depending on the magnitude of the magnetic deflections. Similar bounds, in the range $(0.2 - 7) \times 10^{-4}$ Mpc$^{-3}$, were obtained for sources following the local matter distribution.