Positron Annihilation in the Milky Way and beyond
  The electron-positron annihilation gamma-ray signal at 511 keV in the Milky
Way is investigated towards a possible dark matter interpretation. If all bulge
positrons were created by dark matter particle annihilation, the satellite
galaxies of the Milky Way, apparently being dominated by dark matter, should
also show measurable 511 keV signals. Using INTEGRAL/SPI, we test for emission
in 39 neighbouring dwarf satellite galaxies, and found a consistent trend
against a dark matter scenario. One galaxy, Reticulum II, shows up as a strong
source of annihilation emission, which we interpret as the presence of a
microquasar, ejecting pair-plasma into the galaxy's interstellar medium.
