ner gave an interesting talk describing new work on this subject done in collaboration with graduate student Meng Su (Su & Finkbeiner 2012, posted on the arXiv on June 7). They bring a few new tools to bear on the problem and report “strong evidence” for a detection of line emission from the Galactic center (~5-6σ confidence; see figure below).
First, they make maps showing all the photons Fermi has detected in its 3.7 yr of surveying the entire sky, once every 3 hrs (see figure below). They use these maps to model the spatial distribution of background gamma-ray emission unrelated to the purported line. Subtracting the model, they make another map showing where the excess line emission is actually coming from. They find that the 130 GeV photons above the background are coming from near the Galactic center, although significantly offset by ~2 degrees. The authors go through a variety of analyses to demonstrate that the emission has an astrophysical origin rather than being a bogus instrumental effect.
They fit this excess line emission with a variety of models. The model that fits best represents the dark matter annihilation source as the square of the density distribution of dark matter in the Milky Way (using an Einasto profile) projected along our line of sight, but off-center by that curious 2 degrees. It’s possible that the annihilation source could be pulled off-center by dynamics relating to the Milky Way’s bar, but it’s also possible that that the line emission could be produced by an astrophysical source other than dark matter annihilation at the Galactic center.
Regardless of its source, it’s important to remember that all of this discussion of line emission is based on Fermi’s detection of ~50 photons near 130 GeV from near the Galactic Center. Finkbeiner was clear in his talk that he does not consider this a “discovery,” but he advocates for more resources to study the issue. Su & Finkbeiner suggest altering the survey strategy of the Fermi telescope; they say that if it spent 40% of its time looking at the Galactic center in a way optimized for high energy-resolution, the question of line emission could be answered definitively with just one more year of observations.