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J.M. Silvis (RITSS \& GSFC), A.A. Moiseev (USRA \& GSFC), J.P. Norris, J.F. Ormes, S.M. Ritz (NASA GSFC), GLAST Collaboration
The nature of dark matter is one of the most important unresolved problems in cosmology. Big Bang nucleosynthesis puts an upper limit of 15 matter, while arguments based on galactic rotation curves require some form of dark matter. A leading non-baryonic candidate is the lightest supersymmetric particle, the neutralino. Neutralino annihilations may have observable branching fractions into two gammas or gamma and Z boson, resulting in a mono-energetic photon signature. Predictions of the resulting flux are a few 10-11 cm-2 s-2 sr-1, accessible with sufficiently good energy resolution. Observable rates of gammas would be in the 30-300 GeV energy range, which is unexplored astrophysical territory for line radiation. The CsI calorimeter of the Gamma Ray Large Area Space Telescope (GLAST) can contain enough of the EM showers of obliquely-entering gamma rays to energies well over 300 GeV, for path lengths in the calorimeter (170 cm width X 19 cm depth) greater than 20 radiation lengths (37 cm). Using GLAST simulations, we have developed a selection technique, based only on information available from event reconstruction, that accepts events with sufficient path length to afford ~ 2 achievable energy resolution will depend upon perfection of shower profiling techniques. Selected events will have good enough trajectory information from the GLAST tracker and calorimeter to reject charged particle backgrounds, in combination with the segmented anticoincidence detector. Thus GLAST may be able to probe a wide range of neutralino annihilation models, and possibly resolve lines produced by the two annihilation modes.
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