In my last blog entry I noted that the Fermi Gamma-ray Telescope collaboration, based on two years of data reduction, was reporting that they had not detected a dark matter signal. They employed a method of looking for gamma rays from nearby dwarf galaxies; these are expected to be good targets due to lack of other gamma ray sources and expected high relative density of dark matter. The team examined gamma ray energies up to 100 GeV and found nothing significant (a proton rest mass energy is just under .94 GeV and 1 GeV is a billion electron volts).
But now just in the past 2 weeks we have an independent author who has examined the publicly available Fermi data for gamma rays emitted from our own Galactic center. He was able to analyze around 3.5 years of data, more than the 2 years’ worth of dwarf galaxy data analyzed. It’s just a little bump in the spectrum (see the central region of the figure below), but he claims to see a positive signal at 130 GeV and with a (marginal) statistical significance just in excess of 3 standard deviations. This is tantalizing, potentially, but not strong enough for a clear detection.
This possible signal is also found at a much higher mass than the neighborhood of 10 GeV where COGENT and DAMA/LIBRA have claimed direct detection in Earth-bound laboratory experiments. The plot thickens and as usual we have to wait for more data from FERMI and other experiments.
http://arxiv.org/pdf/1204.2797v1.pdf – Preprint by Christoph Weniger, “A Tentative Gamma-Ray Line from Dark Matter Annihilation at the Fermi Large Area Telescope”