High Energy Emission from the Starburst Galaxy NGC253

TL;DR

This paper models high-energy gamma-ray emission from NGC253 using a detailed numerical approach, predicting flux levels detectable by current gamma-ray telescopes and validating the model with observed radio data.

Contribution

It introduces a comprehensive numerical model for gamma-ray emission in NGC253, integrating hadronic and leptonic processes with observational data for normalization.

Findings

Predicted gamma-ray fluxes are within detectable range of Fermi and Cherenkov telescopes.

Model successfully reproduces observed radio emission, validating the propagation and emission assumptions.

Provides detailed energy distributions of electrons and protons in the starburst galaxy.

Abstract

Measurement sensitivity in the energetic gamma-ray region has improved considerably, and is about to increase further in the near future, motivating a detailed calculation of high-energy (>100 MeV) and very-high-energy (VHE: >100 GeV) gamma-ray emission from the nearby starburst galaxy NGC253. Adopting the convection-diffusion model for energetic electron and proton propagation, and accounting for all the relevant hadronic and leptonic processes, we determine the steady-state energy distributions of these particles by a detailed numerical treatment. The electron distribution is directly normalized by the measured synchrotron radio emission from the central starburst region; a commonly expected theoretical relation is then used to normalize the proton spectrum in this region. Doing so fully specifies the electron spectrum throughout the galactic disk, and with an assumed spatial profile of the magnetic field, the predicted radio emission from the full disk matches well the observed spectrum, confirming the validity of our treatment. The resulting radiative yields of both particles are calculated; the integrated HE and VHE fluxes from the entire disk are predicted to be f(>100 MeV)~2x10^-8 cm^-2 s^-1 and f(>100 GeV)~4x10^-12 cm^-2 s^-1, respectively. We discuss the feasibility of measuring emission at these levels with the space-borne Fermi and the ground-based Cherenkov telescopes.