Systematic effects in the estimate of the local gamma-ray emissivity

TL;DR

This paper highlights significant uncertainties in estimating local gamma-ray emissivity due to various cosmic-ray and interstellar factors, questioning the relevance of the nuclear enhancement factor with recent measurements.

Contribution

It systematically analyzes the uncertainties affecting gamma-ray emissivity estimates and challenges the traditional use of the nuclear enhancement factor based on new cosmic-ray data.

Findings

Uncertainties in gamma-ray emissivity are comparable to current Fermi measurements.

Primary cosmic-ray fluxes and cross-sections significantly influence emissivity estimates.

The nuclear enhancement factor is no longer relevant given recent cosmic-ray measurements.

Abstract

We show in this letter that estimates of the local emissivity of {\gamma}-rays in the GeV-TeV range suffer uncertainties which are of the same order of magnitude as the current Fermi results. Primary cosmic-ray fluxes, cosmic-ray propagation, interstellar helium abundance and {\gamma}-ray production crosssections all affect the estimate of this quantity. We also show that the so-called nuclear enhancement factor -- though widely used so far to model the {\gamma}-ray emissivity -- is no longer a relevant quantity given the latest measurements of the primary cosmic ray proton and helium spectra.