A DARK MATTER HALO AS SOURCE OF GAMMA-RAYS?

Image: Illustration of a dark matter halo around the Milky Way. Credit: ESO/L. Calçada.

The gamma-ray source 3FGL J2212.5+0703 shows evidence of being spatially extended.

In a recent paper (Bertoni et al. 2016) the authors use a large sample of active galactic nuclei and other known gamma-rays sources as a control group, confirming, as expected, that statistically significant extension is rare among such objects.

They argue that the most likely (non-dark matter) explanation for this apparent extension is a pair of bright gamma-ray sources that serendipitously lie very close to each other, and estimate that there is a chance probability of ~2% that such a pair would exist somewhere on the sky.

If a gamma-ray source without detectable emission at other wavelengths were unambiguously determined to be spatially extended, it could not be explained by known astrophysics, and would constitute a smoking gun for dark matter particles annihilating in a nearby subhalo.

The authors assess that if 3FGL J2212.5+0703 is a dark matter subhalo, it would imply that dark matter particles have a mass of ∼18^-33 GeV and an annihilation cross section on the order of σv ∼ 10⁻²⁶ cm³/s, similar to the values required to generate the Galactic Center gamma-ray excess.

Although the information available does not allow to determine the mass of or distance to this subhalo, simulations suggest that the first gamma-ray detected subhalos could plausibly be on the scale of an ultra-faint dwarf galaxy located at a distance of ~10 kpc, or a much smaller clump of dark matter residing within a few tens of parsecs of the Solar System.

• Bertoni et al. 2016 - Is The Gamma-Ray Source 3FGL J2212.5+0703 A Dark Matter Subhalo? (arXiv)