The diffuse gamma-ray background from type Ia supernovae

Amy Lien, Brian D. Fields

Research output: Contribution to journalArticlepeer-review


The origin of the diffuse extragalactic gamma-ray background (EGB) has been intensively studied but remains unsettled. Current popular source candidates include unresolved star-forming galaxies, starburst galaxies, and blazars. In this paper, we calculate the EGB contribution from the interactions of cosmic rays accelerated by TypeIa supernovae (SNe), extending earlier work that only included core-collapse SNe. We consider TypeIa events not only in star-forming galaxies, but also in quiescent galaxies that lack star formation. In the case of star-forming galaxies, consistently including TypeIa events makes little change to the star-forming EGB prediction, so long as both SN types have the same cosmic-ray acceleration efficiencies in star-forming galaxies. Thus, our updated EGB estimate continues to show that star-forming galaxies can represent a substantial portion of the signal measured by Fermi. In the case of quiescent galaxies, conversely, we find a wide range of possibilities for the EGB contribution. The dominant uncertainty we investigated comes from the mass in hot gas in these objects, which provides targets for cosmic rays; total gas masses are as yet poorly known, particularly at larger radii. Additionally, the EGB estimation is very sensitive to the cosmic-ray acceleration efficiency and confinement, especially in quiescent galaxies. In the most optimistic allowed scenarios, quiescent galaxies can be an important source of the EGB. In this case, star-forming galaxies and quiescent galaxies together will dominate the EGB and leave little room for other contributions. If other sources, such as blazars, are found to have important contributions to the EGB, then either the gas mass or cosmic-ray content of quiescent galaxies must be significantly lower than in their star-forming counterparts. In any case, improved Fermi EGB measurements will provide important constraints on hot gas and cosmic rays in quiescent galaxies.

Original languageEnglish (US)
Article number120
JournalAstrophysical Journal
Issue number2
StatePublished - Mar 10 2012


  • cosmic rays
  • gamma rays: diffuse background
  • gamma rays: galaxies
  • supernovae: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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