A POSITRON-ANNIHILATION RADIATION TELESCOPE USING LAUE DIFFRACTION IN A CRYSTAL LENS

We present a new type of gamma-ray telescope featuring a Laue diffraction lens, a detector module with a 3 X 3 germanium array, and a balloon gondola stabilized to 5'' pointing accuracy. The instrument's lens is designed to collect 51 1 keV photons on its 150 cm2 effective area and focus them onto a small detector having only approximately 14 cm3 of equivalent volume for background noise. As a result, this telescope overcomes the mass-sensitivity impasse of present detectors where the collection area is identical to the detection area. The sensitivity of our instrument is anticipated to be 3 X 10(-5) photons cm-2 s-1 at 511 keV with an angular resolution of 15'' and an energy resolution of 2 keV. These features will allow us to resolve a possible narrow 51 1 keV both energetically and spatially within a Galactic center ''microquasar'' such as 1E 1740.7-2942 or GRS 1758-258. Besides the Galactic ''microquasar,'' other prime objectives include Cygnus X-1, X-ray binaries and pulsars.