Influence of extragalactic magnetic fields on extragalactic cascade gamma-ray emission

TL;DR

This paper examines how extragalactic magnetic fields influence gamma-ray emission from electromagnetic cascades caused by ultra-high energy cosmic rays, finding minimal impact in certain energy ranges which simplifies modeling efforts.

Contribution

It provides an analysis showing that magnetic fields have limited effect on cascade gamma-ray spectra in the 10^7-10^9 eV range, aiding dark matter searches.

Findings

Magnetic fields weakly affect cascade emission in the 10^7-10^9 eV range.

Cascade spectra are similar regardless of magnetic field strength within studied ranges.

Simplifies the modeling of gamma-ray background for dark matter detection.

Abstract

We discuss the influence of extragalactic magnetic fields on the intensity of gamma-ray emission produced in electromagnetic cascades from ultra-high energy cosmic rays propagating in extragalactic space. Both cosmic rays and cascade particles propagate mostly out of galaxies, galactic clusters, and large scale structures as their relative volume is small. Therefore their magnetic fields weakly affect emission produced in cascades. Yet estimates of this influence can be useful searching for dark matter particles, when components of extragalactic gamma-ray background should be known, including cascade gamma-ray emission. To study magnetic field influence on cascade emission we analyze cosmic particle propagation in fields of ~10^(-6) and 10^(-12) G (the former is typical inside galaxies and clusters and the latter is common in voids and outside galaxies and clusters). The calculated spectra of cascade gamma-ray emission are similar in the range of ~10^7-10^9 eV. So analyzing cascade emission in this range it is not necessary to specify models of extragalactic magnetic field.