High Energy Emission from the Starburst Galaxy NGC253
  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.
