VHE emission from M82

TL;DR

This paper evaluates the potential for detecting very-high-energy gamma-ray emission from the starburst galaxy M82, using models and current/future telescopes, based on cosmic-ray interactions and existing radio data.

Contribution

It provides the first detailed semi-quantitative and numerical estimates of VHE gamma-ray flux from M82, considering both hadronic and leptonic processes.

Findings

Estimated VHE flux >100 GeV: 2E-12 1/(cm^2 s)

Estimated flux >100 MeV: 1E-8 1/(cm^2 s)

Potential detectability by MAGIC, VERITAS, and GLAST/LAT

Abstract

Spurred by the improved measurement sensitivity in the very-high-energy (VHE: >100 GeV) gamma-ray band, we assess the feasibility of detection of the nearby starburst galaxy M82. VHE emission is expected to be predominantly from the decay of neutral pions which are produced in energetic proton interactions with ambient protons. An estimate of VHE emission from this process is obtained by an approximate, semi-quantitative calculation, and also by a detailed numerical treatment based on a convection-diffusion model for energetic electron and proton propagation and energy losses. All relevant hadronic and leptonic processes are considered, gauged by the measured synchrotron radio emission from the inner disk region. We estimate an integrated flux f(>100 GeV) 2E-12 1/(cm^2 s), possibly detectable by the current northern-hemisphere imaging air Cherenkov telescopes, MAGIC and VERITAS, and a good candidate for detection with the upcoming MAGIC II telescope. We also estimate f(>100 MeV) E-8 1/(cm^2 s), a level of emission that can be detected by GLAST/LAT based on the projected sensitivity for a one-year observation.