The pionic contribution to diffuse γ-rays: Upper limits

Tijana Prodanović, Brian D. Fields

Research output: Contribution to journalArticlepeer-review


Diffuse γ-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 γ-ray spectra at in the energy range 50 MeV≲Eγ≲10 GeV. The hadronic component is dominated by emission from neutral pions, with a characteristic spectrum symmetric about mπ0/2. We exploit the well-defined properties of the pion decay spectrum to quantify the maximum pionic fraction of the observed γ-ray intensity. We find that the Galactic spectrum above 30 MeV can be atmost 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 γ-ray and neutrino emission are briefly discussed.

Original languageEnglish (US)
Pages (from-to)627-635
Number of pages9
JournalAstroparticle Physics
Issue number6
StatePublished - Sep 2004


  • Abundances
  • Cosmic-rays
  • Nuclear reactions
  • Nucleosynthesis
  • γ-rays

ASJC Scopus subject areas

  • Astronomy and Astrophysics


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