Nuclear enhancement of the photon yield in cosmic ray interactions

TL;DR

This paper refines the calculation of the nuclear enhancement factor in cosmic ray interactions, crucial for accurate gamma-ray background modeling in astrophysics, by incorporating spectral averaging effects using advanced interaction models.

Contribution

It introduces a new calculation method for the nuclear enhancement factor that accounts for spectral averaging, improving the accuracy of gamma-ray emission models.

Findings

Revised nuclear enhancement factor values using QGSJET-II-04 and EPOS-LHC models.

Identification of the importance of spectral averaging in gamma-ray production.

Enhanced background models for gamma-ray astronomy.

Abstract

The concept of the nuclear enhancement factor has been used since the beginning of gamma-ray astronomy. It provides a simple and convenient way to account for the contribution of nuclei (A>1) in cosmic rays (CRs) and in the interstellar medium (ISM) to the diffuse gamma-ray emission. An accurate treatment of the dominant emission process, such as hadronic interactions of CRs with the ISM, enables one to study CR acceleration processes, CR propagation in the ISM, and provides a reliable background model for searches of new phenomena. The Fermi Large Area Telescope (Fermi-LAT) launched in 2008 provides excellent quality data in a wide energy range 30 MeV - 1 TeV where the diffuse emission accounts for the majority of photons. Exploiting its data to the fullest requires a new study of the processes of gamma-ray production in hadronic interactions. In this paper we point out that several commonly used studies of the nuclear enhancement factor miss to account for the spectrally averaged energy loss fraction which ensures that the energy fraction transferred to photons is averaged properly with the spectra of CR species. We present a new calculation of the spectrally averaged energy loss fraction and the nuclear enhancement factor using the QGSJET-II-04 and EPOS-LHC interaction models.