Fermi constrains dark-matter origin of high-energy positron anomaly

Martin Pohl, David Eichler

Research output: Contribution to journalArticlepeer-review


Fermi measurements of the high-latitude γ-ray background strongly constrain a decaying-dark-matter origin for the 1-100GeV Galactic positron anomaly measured with PAMELA. Inverse Compton scattering of the microwave background by the emergent positrons produces a bump in the diffuse 100-200 MeV γ-ray background that would protrude from the observed background at these energies. The positrons are thus constrained to emerge from the decay process at a typical energy between ∼ 100GeV and ∼ 250GeV. By considering only γ-ray emission of the excess positrons and electrons, we derive a minimum diffuse γ-ray flux that, apart from the positron spectrum assumed, is independent of the actual decay modes. Any γ-rays produced directly by the dark-matter decay leads to an additional signal that makes the observational limits more severe. A similar constraint on the energy of emergent positrons from annihilation in dark-matter substructures is argued to exist, according to recent estimates of enhancement in low-mass dark-matter substructures, and improved simulations of such substructure will further sharpen this constraint.

Original languageEnglish
Pages (from-to)L53-L57
JournalAstrophysical Journal Letters
Issue number1 PART 2
StatePublished - 1 Jan 2010


  • Cosmic rays
  • Dark matter
  • Gamma rays: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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