  The observed angular profile of the 511-keV photon excess from the Milky Way
galactic center can allow us to select among combinations of various dark
matter and other positron production mechanisms with various models for the
dark matter distribution. We find that a relic decay scenario gives too flat an
angular distribution for any dark matter distribution in our survey, but that a
dark matter-dark matter collisional scenario, or a scenario that involves
particles emitted from a localized central source producing positrons some
distance out, can match the observed galactic center angular profile if the
dark matter distribution is neither too flat nor too cuspy. Additionally,
positron migration or diffusion before annihilation broadens the angular
profile to an extent that an average migration of more than half a kiloparsec
is not viable with most dark matter distributions. The observed angular profile
is also consistent with the occurrence of transient events in the past,
followed by isotropic positron diffusion.
