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 ( HE : \geq 100 MeV ) and very-high-energy ( VHE : \geq 100 GeV ) \gamma -ray emission from the nearby starburst galaxy NGC 253 .
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 ( \geq 100 { MeV } ) \simeq ( 1.8 ^ { +1.5 } _ { -0.8 } ) \times 10 ^ { -8 } cm ^ { -2 } s ^ { -1 } , and f ( \geq 100 { GeV } ) \simeq ( 3.6 ^ { +3.4 } _ { -1.7 } ) \times 10 ^ { -12 } cm ^ { -2 } s ^ { -1 } , with a central magnetic field value B _ { 0 } \simeq 190 \pm 10 \mu G. We discuss the feasibility of measuring emission at these levels with the space-borne Fermi and ground-based Cherenkov telescopes .