A nearby source of ultra-high energy cosmic rays

TL;DR

This paper establishes that the nearest source of ultra-high energy cosmic rays emitting heavy nuclei must be within 5 Mpc, providing new bounds on source distance and density based on recent high-energy cosmic ray observations.

Contribution

It introduces the first constraints on the number density of UHECR sources emitting heavy nuclei and derives an upper limit on the distance to the closest such source.

Findings

Closest UHECR source within 5 Mpc at 95% C.L.

Lower bound on source density: > 1.0 x 10^{-4} Mpc^{-3}.

Constraints on heavy nuclei UHECR source distribution.

Abstract

Recently the Telescope Array collaboration reported an observation of cosmic ray event with very high energy 244 EeV ($2.44 \times 10^{20}$ eV). Importantly, the event is hard to correlate with the matter distribution in the local Universe, even after taking into account deflections in magnetic fields. This implies that the event is likely a nucleus with a large charge. An attenuation length of the nucleus of such a high energy in intergalactic space is quite small, therefore its source should be relatively close to our Galaxy. Using these arguments we derive a new upper bound on a distance to the closest ultra-high energy cosmic ray (UHECR) source and a lower bound on the UHECR source number density in general. The distance to the closest source should not exceed 5 Mpc at 95% C.L. and the 95% C.L. lower-bound on the sources number density is $\rho > 1.0 \times 10^{-4}$ Mpc$^{-3}$. The number density of UHECR sources emitting heavy nuclei is constrained for the first time.