# The influence of the observatory latitude on the study of ultra high energy cosmic rays

## TL;DR

This paper investigates how the latitude of cosmic ray observatories affects measurements of ultra high energy cosmic rays, impacting flux detection and anisotropy analysis, based on simulated arrival direction distributions and real survey data.

## Contribution

It quantifies the influence of observatory latitude on flux measurements and anisotropy detection capabilities in UHECR studies.

## Key findings

- Latitude affects the total flux measured by observatories.
- Latitude imposes limitations on anisotropy measurement capabilities.
- Differences between northern and southern hemisphere observatories are significant.

## Abstract

Recent precision measurements of the Ultra High Energy Cosmic Rays (UHECR) arrival directions, spectrum and parameters related to the mass of the primary particle have been done by the HiRes, Pierre Auger and Telescope Array (TA) Observatories. In this paper, distributions of arrival directions of events in the nearby Universe are assumed to correlate with sources in the 2MASS Redshift Survey (2MRS), IRAS 1.2 Jy Survey, Palermo Swift-BAT and Swift-BAT catalogs, and the effect of the latitude of the observatory on the measurement of the energy spectrum and on the capability of measuring anisotropy is studied. The differences between given latitudes on the northern and southern hemispheres are quantified. It is shown that the latitude of the observatory: a) has an influence on the total flux measured and b) imposes an important limitation on the capability of measuring an anisotropic sky.