A study of the Correlation of Arrival Directions of UHECRs with the Large Scale Structure of the Universe

TL;DR

This study uses simulations to analyze how magnetic fields in the universe affect the correlation between ultra-high-energy cosmic ray arrival directions and their sources, comparing results with observational data.

Contribution

It introduces a detailed simulation of UHECR propagation considering intergalactic magnetic fields based on turbulence dynamo models, providing insights into source identification challenges.

Findings

Magnetic deflections significantly obscure source correlations.

Simulated angular distributions are comparable to Auger data.

Implications for the nature and location of UHECR sources.

Abstract

Ultrahigh energy cosmic rays (UHECRs) are believed to originate from astrophysical sources, which should trace the large scale structure (LSS) of the universe. On the other hand, the magnetic field in the intergalactic space (IGMF), which also traces the LSS of the universe, deflects the trajectories of the charged UHECRs and spoils the positional correlation of the observed UHECR events with their true sources. To explore this problem, we studied a simulation of the propagation of UHE protons through the magnetized LSS of the universe, reported earlier in Das et al. (2008), in which the IGMF was estimated based on a turbulence dynamo model (Ryu et al. 2008). Hypothetical sources were placed inside clusters and groups of galaxies in the simulated universe, while observers were located inside groups of galaxies that have similar properties as the Local Group. We calculated the statistics of the angular distance between the arrival directions of simulated UHE proton events and the positions of candidate sources in our simulation. We compared the statistics from our simulation with those calculated with the Auger data. We discussed the implication of our works on the nature of the sources of UHECRs.