Towards the first light for a gamma-ray lens

The ``gamma-ray lens'' collaboration is presently preparing for a fundamentally new type of telescope, which is to be flown on a statospheric balloon by the French Space Agency CNES. The instrument features a Laue diffraction lens, a detector module with a 3x3 germanium array, and a balloon gondola stabilized to 15'' pointing accuracy. The first flight is planned for the 2 end of 1999 from Leon, Spain. The instrument's lens focusses gamma-ray photons from its 600 cm area onto a small solid state detector, with only 18 cm(3) equivalent volume for background noise. Besides its excellent sensitivity, the telescope has outstanding angular and spectral resolution. The primary objective for its first balloon Right is to detect the Crab nebula and to measure its angular extent at 170 keV with an unprecedented angular resolution of about 1 are minute. For the first time in gamma-ray astronomy, the statistics will be dominated by the signal: for a residual atmosphere of 5.5 g/cm(2) and during a balloon Right at mid-latitudes, the observation of the Crab is expected to be essentially background free. The background will be only a few count/hour, with a detected source Bur of 25 to 40 photons per hour at the Crab culmination. Scientific objectives for further flights include collapsed objects, SNRs, and broad class annihilators.