The origin of the cosmic gamma-ray background in the MeV range

TL;DR

This study evaluates the contribution of Type Ia supernovae to the cosmic gamma-ray background in the MeV range, incorporating recent models and measurements, and finds they account for up to half of the observed flux.

Contribution

It provides a comprehensive analysis using advanced 3D explosion models and new high-redshift supernova rates to reassess SNe Ia's role in the gamma-ray background.

Findings

SNe Ia contribute up to 30-50% of the gamma-ray background.

Standard models underestimate the SNe Ia contribution without systematic errors.

Other sources like FSRQs are consistent with the observed flux levels.

Abstract

There has been much debate about the origin of the diffuse $\gamma$--ray background in the MeV range. At lower energies, AGNs and Seyfert galaxies can explain the background, but not above $\simeq$0.3 MeV. Beyond $\sim$10 MeV blazars appear to account for the flux observed. That leaves an unexplained gap for which different candidates have been proposed, including annihilations of WIMPS. One candidate are Type Ia supernovae (SNe Ia). Early studies concluded that they were able to account for the $\gamma$--ray background in the gap, while later work attributed a significantly lower contribution to them. All those estimates were based on SN Ia explosion models which did not reflect the full 3D hydrodynamics of SNe Ia explosions. In addition, new measurements obtained since 2010 have provided new, direct estimates of high-z SNe Ia rates beyond $z\sim$2. We take into account these new advances to see the predicted contribution to the gamma--ray background. We use here a wide variety of explosion models and a plethora of new measurements of SNe Ia rates. SNe Ia still fall short of the observed background. Only for a fit, which would imply $\sim$150\% systematic error in detecting SNe Ia events, do the theoretical predictions approach the observed fluxes. This fit is, however, at odds at the highest redshifts with recent SN Ia rates estimates. Other astrophysical sources such as FSRQs do match the observed flux levels in the MeV regime, while SNe Ia make up to 30--50\% of the observed flux.