Observability of Gamma Rays from Dark Matter Neutralino Annihilations in the Milky Way Halo

Recent advances in N-body simulations of cold dark matter halos point to a substantial density enhancement near the center. This means that, e.g., the $\gamma$ ray signals from neutralino dark matter annihilations would be significantly enhanced compared to old estimates based on an isothermal sphere model with large core radius. Another important development concerns new detectors, both space- and ground-based, which will cover the window between 50 and 300 GeV where presently no cosmic $\gamma$-ray data are available. Thirdly, new calculations of the $\gamma$-ray line signal (a sharp spike of $10^{-3}$ relative width) from neutralino annihilations have revealed a hitherto neglected contribution which, for heavy higgsino-like neutralinos, gives an annihilation rate an order of magnitude larger than previously predicted. We make a detailed phenomenological study of the possible detection rates given these three pieces of new information. We show that the proposed upgrade of the Whipple telescope will make it sensitive to a region of parameter space, with substantial improvements possible with the planned new generation of Air Cherenkov Telescope Arrays. We also comment on the potential of the GLAST satellite detector. An evaluation of the continuum $\gamma$-rays produced in neutralino annihilations into the main modes is also done. It is shown that a combination of high-rate models and very peaked halo models are already severely constrained by existing data.Comment: 44 pages, LaTex, eps figures embedded with epsfig and subfigure macro