MILLISECOND PULSAR ORIGIN OF THE GALACTIC CENTER GEV EXCESS

Image: The Milky Way. Credit: Serge Brunier

Using γ-ray data from the Fermi Large Area Telescope, various groups have identified a clear excess emission in the inner Galaxy, at energies around a few GeV. This excess attracted great attention, because it has properties typical for a dark matter annihilation signal.

Proposed diffuse emission mechanisms, like leptonic or hadronic outbursts or cosmic-ray injection in the central molecular zone, potentially explain part of the excess emission. However, it is challenging to explain all of the above aspects of the GCE with these mechanisms alone.

The most plausible astrophysical interpretation for the Galactic center eccess (GCE) is the combined emission from a large number of unresolved millisecond pulsars (MSPs) in the Galactic bulge region. Recently, it was shown that the spatial distribution of MSPs that were spilled out of disrupted globular clusters can explain the morphology of the GCE.

Image: SNR of the wavelet transform
of γ-rays with energies in the range 1-4 GeV.
Credit: Bartels et al. 2016

In a rencent paper (Bartels et al. 2016), using almost seven years of Fermi-LAT data, the authors detect a clustering of photons as predicted for the hypothetical population of millisecond pulsar, with a statistical significance of 10,8 σ. For plausible values of the luminosity function, this population explains 100% of the observed excess emission.

The authors argue that other extragalactic or Galactic sources, a mismodeling of Galactic diffuse emission, or the thick-disk population of pulsars are unlikely to account for this observation.

The paper (Bartels et. al 2016) is available online and is published in the PhRvL >>
http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.051102
http://arxiv.org/pdf/1506.05104v2.pdf

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