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Evidence Against a Dark Matter Explanation of the Galactic Center gamma-ray excess
October 12, 20171:15 pm – 2:15 pm (CDT)

Evidence Against a Dark Matter Explanation of the Galactic Center gamma-ray excess


Oscar Macias (Virginia Tech)



Mitchell Institute for Fundamental Physics & Astronomy

College Station, Texas 77843

Event Details

An anomalous, apparently diffuse, gamma-ray signal not readily attributable to known Galactic sources has been found in Fermi space telescope data covering the central ~10 degrees of the Galaxy. This “Galactic Center Gamma-Ray Excess” (GCE) signal has a spectral peak at ~2 GeV and reaches its maximum intensity at the Galactic Centre (GC) from where it falls off as a radial power law ~r^{-2.4}. Given its morphological and spectral characteristics, the GCE is ascribable to self-annihilation of dark matter particles governed by an Navarro-Frenk-White-like density profile. However, it could also be composed of many dim, unresolved point sources for which millisecond pulsars (MSPs) or pulsars would be natural candidates given their GeV-peaked spectra. Statistical evidence that many subthreshold point sources contribute up to 100% of the GCE signal has recently been claimed. We have developed a novel analysis that exploits hydrodynamical modelling to better register the position of gamma-ray emitting gas in the Inner Galaxy. Our improved analysis reveals that the excess gamma-rays are correlated with the stellar over-density in the Galactic bulge and the nuclear stellar bulge. Given these correlations, we argue that the GC excess is not a dark matter phenomenon but rather associated with the stellar structures present in the Galactic Center.

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