Diffuse non-thermal emission in the disks of the Magellanic Clouds

TL;DR

This study models the non-thermal radio and gamma-ray emission in the Magellanic Clouds, revealing a primarily hadronic origin of gamma rays and detailed contributions from various radiative processes.

Contribution

It provides a comprehensive, self-consistent model of the non-thermal emission in the Magellanic Clouds based on recent radio and gamma-ray data, including neutrino flux predictions.

Findings

Radio emission has primary, secondary, and thermal origins.

Gamma rays mainly from neutral-pion decay with some bremsstrahlung and scattering.

Proton spectra are similar in both galaxies with spectral index ~2.4.

Abstract

The Magellanic Clouds, two dwarf galaxy companions to the Milky Way, are among the Fermi Large Area Telescope (LAT) brightest gamma-ray sources. Aiming at a comprehensive modeling of the non-thermal electromagnetic and neutrino emission in both Clouds, we self-consistently model the radio and gamma-ray spectral energy distribution from their disks based on recently published Murchison Widefield Array and Fermi/LAT data. All relevant radiative processes involving relativistic and thermal electrons (synchrotron, Compton scattering, and bremsstrahlung) and relativistic protons (neutral-pion decay following interaction with thermal protons) are considered, using exact emission formulae. Our joint spectral analyses indicate that radio emission in the Clouds has both primary and secondary electron synchrotron and thermal bremsstrahlung origin, whereas gamma rays originate mostly from neutral-pion decay with some contributions from relativistic bremsstrahlung and Compton scattering off starlight. The proton spectra in both galaxies are modeled as power laws in energy with similar spectral indices, ~2.4, and energy densities, ~1 eV/cm3. The predicted 0.1-10 GeV neutrino flux is too low for detection by current and upcoming experiments. Our analyses confirm earlier suggestions of a largely hadronic origin of the gamma-ray emission in both Magellanic Clouds.