Dark matter subhalos as Fermi gamma-ray sources and first candidates in the 1FGL catalog

Abstract

Predicted by hierarchical structure formation, Milky Way-type galaxies are anticipated to host numerous dark matter subhalos with masses between 10^{10} and a cut-off of 10^{-6} solar masses, or even less. In self-annihilating dark matter scenarios, these objects could be visible in the gamma-ray band as faint and non-variable sources without astrophysical counterpart. In accordance with realistic subhalo models and current observational constraints on self-annihilating dark matter, we predict that about one massive Galactic subhalo may have already been detected in the 11-months catalog of Fermi-LAT data (1FGL). Selection cuts applied to the 1FGL reveal twelve possible candidates, and in-depth studies of the most promising object, 1FGL J0030.7+0724, are presented. In a dedicated X-ray follow-up observation with the Swift XRT, seven point-like X-ray sources have been discovered. Within the positional uncertainty derived from the 24-months Fermi-LAT data, we consider the unidentified radio source NVSS J003119+072456, coinciding with one of the discovered Swift sources, as the most promising counterpart candidate for 1FGL J0030.7+0724. The broad-band spectral energy distribution is consistent with a high-energy-peaked blazar. However, flux and extent of the Fermi source may also be compatible with a dark matter subhalo. A discrimination between the two scenarios requires further multi-wavelength observations. Strategies for identifying gamma-ray sources associated with self-annihilating DM subhalos are discussed.