Astronomy and Astrophysics – Astrophysics
Scientific paper
2004-03-12
Astropart.Phys. 21 (2004) 627-635
Astronomy and Astrophysics
Astrophysics
14 pages, 4 figures, AASTeX. Comments welcome
Scientific paper
10.1016/j.astropartphys.2004.04.
Diffuse gamma rays probe the highest-energy processes at the largest scales. Here we derive model-independent constraints on the hadronic contribution to the Galactic and extragalactic gamma-ray spectra in the energy range 50 MeV < E_gamma < 10 GeV. The hadronic component is dominated by emission from neutral pions, with a characteristic spectrum symmetric about m_{pi^0}/2. We exploit the well-defined properties of the pion decay spectrum to quantify the maximum pionic fraction of the observed gamma-ray intensity. We find that the Galactic spectrum above 30 MeV can be at most about 50% pionic. The maximum pionic contribution to the extragalactic spectrum is energy dependent; it also depends on the redshift range over which the sources are distributed, ranging from as low as about 20% for pions generated very recently, to as much as 90% if the pions are generated around redshift 10. The implications of these constraints for models of gamma-ray and neutrino emission are briefly discussed.
Fields Brian D.
Prodanovic Tijana
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