Fermi gamma-ray haze via dark matter and millisecond pulsars

Dmitry Malyshev, Ilias Cholis, Joseph D. Gelfand

Research output: Contribution to journalArticle

Abstract

We study possible astrophysical and dark matter (DM) explanations for the Fermi gamma-ray haze in the Milky Way halo. As representatives of various DM models, we consider DM particles annihilating into W+W-, bb̄, and e+e-. In the first two cases, the prompt gamma-ray emission from DM annihilations is significant or even dominant at E > 10 GeV, while inverse Compton scattering (ICS) from annihilating DM products is insignificant. For the e+e- annihilation mode, we require a boost factor of order 100 to get significant contribution to the gamma-ray haze from ICS photons. Possible astrophysical sources of high-energy particles at high latitudes include type Ia supernovae (SNe) and millisecond pulsars (MSPs). Based on our current understanding of Ia SNe rates, they do not contribute significantly to gamma-ray flux in the halo of the Milky Way. As the MSP population in the stellar halo of the Milky Way is not well constrained, MSPs may be a viable source of gamma-rays at high latitudes provided that there are ∼(2-6) × 104 of MSPs in the Milky Way stellar halo. In this case, pulsed gamma-ray emission from MSPs can contribute to gamma rays around few GeV, while the ICS photons from MSP electrons and positrons may be significant at all energies in the gamma-ray haze. The plausibility of such a population of MSPs is discussed. Consistency with the Wilkinson Microwave Anisotropy Probe (WMAP) microwave haze requires that either a significant fraction of MSP spin-down energy is converted into e+e- flux or the DM annihilates predominantly into leptons with a boost factor of order 100.

Original languageEnglish (US)
Pages (from-to)1939-1945
Number of pages7
JournalAstrophysical Journal
Volume722
Issue number2
DOIs
StatePublished - Oct 20 2010

Keywords

  • Cosmic rays
  • Dark matter
  • Galaxy: halo
  • Gamma rays: diffuse background
  • Pulsars: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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