Gamma-Ray Astronomy Starts to see CLAIRE: First Light for a Crystal Diffraction Telescope

CLAIRE is a balloon-borne experiment dedicated to validating the concept of a diffraction gamma-ray lens. This new concept for high energy telescopes is very promising and could significantly increase sensitivity and angular resolution in nuclear astrophysics. CLAIRE's lens consists of 556 Ge-Si crystals, focusing 170 keV gamma-ray photons onto a 3x3 matrix of HPGe detectors, each detector element being only 1.5 x 1.5 x 4.0 cm(3). On June 14 2001, CLAIRE was launched by the French Space Agency (CNES) from its balloon base at Gap in the French Alps and was recovered near the Atlantic ocean (500 km to the West) after about 5 hours at float altitude. Pointing accuracy allowed for 72 minutes of "good pointing time" on the Crab Nebula. During this time, 33 diffracted photons have been detected leading to a 3 sigma detection of the source. This result, confirmed by other measurements made on the ground (with radioactive sources, x-ray generators and source distances from 14 to 205 m), validates the concept of diffractive gamma-ray lenses for nuclear astrophysics and is the first step towards a space borne instrument.