Analysis of large-scale anisotropy of ultra-high energy cosmic rays in HiRes data

TL;DR

This study analyzes six years of HiRes stereo data to investigate large-scale anisotropy in ultra-high energy cosmic rays, testing models of matter-tracing sources and isotropy, and finds compatibility with isotropy at high energies.

Contribution

It introduces a detailed analysis of large-scale anisotropy in cosmic rays using HiRes data and tests the matter tracer model against isotropy at ultra-high energies.

Findings

Data above 40 EeV disfavors the matter tracer model unless deflections exceed 10 degrees.

Data above 10 EeV is consistent with both isotropic and matter tracer models.

No significant anisotropy detected at energies below 40 EeV.

Abstract

Stereo data collected by the HiRes experiment over a six year period are examined for large-scale anisotropy related to the inhomogeneous distribution of matter in the nearby Universe. We consider the generic case of small cosmic-ray deflections and a large number of sources tracing the matter distribution. In this matter tracer model the expected cosmic ray flux depends essentially on a single free parameter, the typical deflection angle theta. We find that the HiRes data with threshold energies of 40 EeV and 57 EeV are incompatible with the matter tracer model at a 95% confidence level unless theta is larger than 10 degrees and are compatible with an isotropic flux. The data set above 10 EeV is compatible with both the matter tracer model and an isotropic flux.