CLAIRE: First light for a gamma-ray lens

• Published in: Experimental astronomy Vol. 20; no. 1-3; pp. 253 - 267
• Main Authors: Ballmoos, Peter von, Halloin, Hubert, Evrard, Jean, Skinner, Gerry, Abrosimov, Nikolai, Alvarez, Jose, Bastie, Pierre, Hamelin, Bernard, Hernanz, Margarida, Jean, Pierre, Knödlseder, Jürgen, Smither, Bob
• Format: Journal Article
• Language: English
• Published: Springer Link 01-12-2005
• Subjects: Astrophysics; Cosmology and Extra-Galactic Astrophysics; Physics; Sciences of the Universe; Instrumentation; Gamma Ray Optics; Nuclear Astrophysics; Laue Crystals
• ISSN: 0922-6435; 1572-9508
• DOI: 10.1007/s10686-006-9071-0

The objective of the R&D project CLAIRE was to prove the principle of a gamma-ray lens for nuclear astrophysics. CLAIRE's Laue diffraction lens has a diameter of 45 cm and a focal length of 277 cm; 556 germanium-silicon crystals are tuned to focus 170 keV photons onto a 1.5 cm diameter focal spot. Laboratory measurements of the individual crystals and the entire lens have been used to validate a numerical model that we use to estimate the lens performance for a source at infinity. During a stratospheric balloon flight on 2001 June 14, CLAIRE was directed at the Crab nebula by a pointing system able to stabilize the lens to within a few arcseconds of the target. In 72 min of valid pointing time, 33 photons from the Crab were detected in the 3 keV bandpass of the lens: CLAIRE's first light! The performance of CLAIRE's gamma-ray lens, namely the peak reflectivity for a polychromatic source (9±1%), has been confirmed by ground data obtained on a 205 meter long test range. CLAIRE's measured performance validates the principle of a Laue lens for nuclear astrophysics, opening the way for a space-borne gamma-ray lens telescope that will achieve one to two orders of magnitude improvement in sensitivity over present technologies.