$\gamma$-Cascade V4: A Semi-Analytical Code for Modeling Cosmological Gamma-Ray Propagation

TL;DR

This paper introduces an improved semi-analytical code for modeling cosmological gamma-ray propagation, accounting for electromagnetic cascades, redshifting, and various extragalactic radiation fields, with validation against Monte Carlo models.

Contribution

The new code enhances the original $\gamma$-Cascade by improving high-redshift performance, adding propagation modules, and incorporating multiple EBL models to estimate uncertainties.

Findings

Good agreement with Monte Carlo models within EBL uncertainties

Enhanced performance at high redshifts

Ability to estimate uncertainties from different EBL models

Abstract

Since the universe is not transparent to gamma rays with energies above around one hundred GeV, it is necessary to account for the interaction of high-energy photons with intergalactic radiation fields in order to model gamma-ray propagation. Here, we present a public numerical software for the modeling of gamma-ray observables. This code computes the effects on gamma-ray spectra from the development of electromagnetic cascades and cosmological redshifting. The code introduced here is based on the original $\gamma$-Cascade, and builds on it by improving its performance at high redshifts, introducing new propagation modules, and adding many more extragalactic radiation field models, which enables the ability to estimate the uncertainties inherent to EBL modeling. We compare the results of this new code to existing Monte Carlo electromagnetic transport models, finding good agreement within EBL uncertainties.