Gamma-ray emission observed by Fermi-LAT and by VERITAS compared with spectral energy distribution produced by pion decay (dot-dashed line), relativistic bremsstrahlung (dot-dot-dashed) and ICS computed for three different photon fields: CMB (dashed), Galactic background (dotted) and IR photons produced by local warm dust (solid). The thick solid line is the sum of all the contributions. Both Fermi-LAT and VERITAS data points include only statistical errors at 1σ. For VERITAS data the systematic error is found to be ~30% (Acciari et al. 2011), while for Fermi-LAT the systematic uncertainties are comparable to or even larger than the statistical error especially for the lowest energy bins due to difficulties in evaluating the galactic background (see Fig. 3 in Giordano et al. 2012, and the related discussion).