Very-high-energy emission from M 82

¹ INAF – Osservatorio Astronomico di Trieste and INFN-Trieste, via G.B. Tiepolo 11, 34143 Trieste, Italy e-mail: persic@oats.inaf.it
² School of Physics & Astronomy, Tel Aviv University, Tel Aviv 69978, Israel
³ Center for Astrophysics and Space Sciences, University of California at San Diego, La Jolla, CA 92093, USA

Received: 6 February 2008
Accepted: 18 May 2008

Abstract

Spurred by the improved measurement sensitivity in the very-high-energy (VHE: ≥100 GeV) γ-ray band, we assess the feasibility of detection of the nearby starburst galaxy M 82. 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 ≥100 GeV) ~ 2  10^-12 cm^-2 s^-1, 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 ≥100 MeV) ~ 10^-8 cm^-2 s^-1, a level of emission that can be detected by GLAST/LAT based on the projected sensitivity for a one-year observation.