Volume 538, February 2012
|Number of page(s)||16|
|Section||Cosmology (including clusters of galaxies)|
|Published online||09 February 2012|
Dark matter subhaloes as gamma-ray sources and candidates in the first Fermi-LAT catalogue
1 University of Hamburg, Institut für Experimentalphysik, Luruper Chaussee 149, 22761 Hamburg, Germany
2 University of Würzburg, Institut für Theoretische Physik und Astrophysik, Am Hubland, 97074 Würzburg, Germany
Received: 7 July 2011
Accepted: 3 November 2011
The standard paradigm of hierarchical structure formation in a ΛCDM universe predicts the presence of dark matter subhaloes, hosted by Milky Way-sized galaxies. Anticipated subhalo masses range from 1010 down to a cut-off mass between 10-3 and 10-11 M⊙. If dark matter is composed of heavy self-annihilating or decaying particles, these subhaloes could be visible in the γ-ray band as faint and temporally constant sources without astrophysical counterparts. Based upon realistic subhalo models and current observational constraints on annihilating dark matter scenarios, we predict that one massive Galactic subhalo between 106 and 108 M⊙ may already be present in the 11-month catalogue of Fermi-LAT. Indeed, at least twelve objects in the first Fermi catalogue qualify as candidates. The most promising object, 1FGL J0030.7+0724, is investigated in detail using a dedicated Swift X-ray follow-up observation and a refined positional analysis of the 24-month Fermi-LAT data. With the new observations, seven point-like X-ray sources have been discovered, of which SWIFT J003119.8+072454, which coincides with a faint radio source (12 mJy at 1.4 GHz), serves as a counterpart candidate of 1FGL J0030.7+0724. The broad-band spectral energy distribution is consistent with a high-energy-peaked blazar. However, flux and extent of 1FGL J0030.7+0724 may also be compatible with a dark matter subhalo. Detection of temporal variability or improved astrometry of 1FGL J0030.7+0724 are necessary to rule out or confirm an astrophysical origin. We discuss strategies to identify γ-ray sources that are associated with self-annihilating dark matter subhaloes.
Key words: dark matter / Galaxy: halo / Galaxy: structure / gamma rays: general
© ESO, 2012
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