# Cosmic ray ensembles from ultra-high energy photons propagating in the galactic and intergalactic space

## TL;DR

This paper investigates the development and detection prospects of ultra-high energy photon cascades propagating through galactic and intergalactic space, using Monte Carlo simulations to understand their distribution and arrival at Earth.

## Contribution

It presents the first detailed simulation study of ultra-high energy photon cascades in galactic and intergalactic magnetic fields, including their potential detectability.

## Key findings

- Photons in cascades are spread over hundreds of kilometers at Earth's atmosphere.
- Cascades originating 10 Mpc away produce a few correlated photons arriving at Earth.
- Simulation results inform detection strategies with the Cosmic-Ray Extremely Distributed Observatory.

## Abstract

Propagation of ultra-high energy photons in the galactic and intergalactic space gives rise to cascades comprising thousands of photons. Using Monte Carlo simulations, we investigate the development of such cascades in the solar magnetosphere, and find that the photons in the cascades are distributed over hundreds of kilometers as they arrive at the top of the Earth's atmosphere. We also perform similar study for cascades starting as far as 10 Mpc away from us using relevant magnetic field models. A few photons correlated in time are expected to arrive at the Earth from the latter type of cascade. We present our simulation results and discuss the prospects for detection of these cascades with the Cosmic-Ray Extremely Distributed Observatory.