2011MNRAS.414.3577M

Analyses have found a `haze' of anomalous microwave emission surrounding the Galactic Centre in the Wilkinson Microwave Anisotropy Probe (WMAP) sky maps. A recent study using Fermi data detected a similar haze in the γ-ray. Several studies have modelled these hazes as radiation from the leptonic byproducts of dark matter annihilations, and arguably no convincing astrophysical alternative has been suggested. We discuss the characteristics of astrophysical cosmic ray sources that could potentially explain this microwave and γ-ray emission. The most promising astrophysical scenarios involve cosmic ray sources that are clustered such that many fall within ∼1 kpc of the Galactic Centre. For example, we show that several hundred Galactic Centre supernovae in the last million years plus a diffusion-hardened electron spectrum may be consistent with present constraints on this emission. Alternatively, it could be due to a burst of activity probably associated with Sagittarius A* occurring ∼1 Myr ago and producing >10⁵¹ erg in cosmic ray electrons. Different models predict contrasting trends for the spectral index of the microwave and γ-ray spectrum as a function of angle from the Galactic Centre that we show should be robust to cosmic ray propagation uncertainties. In particular, if the haze is from dark matter annihilations, it should have a very hard microwave and γ-ray spectrum for which the spectral shape does not change significantly with angle, which we argue would be difficult to achieve with any astrophysical mechanism. Observations with the Planck and Fermi satellites can distinguish between viable haze models using these signatures.