CREST: A cosmic-ray electron synchrotron telescope to measure tev electrons

The Cosmic Ray Electron Synchrotron Telescope (CREST) instrument is a balloon payload designed to measure the flux of primary cosmic ray electrons at energies greater than 1 TeV. As electrons at these energies lose energy very rapidly during propagation through the interstellar medium, their detection would indicate the existence of sources that are nearby on a Galactic scale. In order to obtain the large exposure time and detector aperture required for this measurement, we use an approach based on the detection of synchrotron photons emitted by electrons in the Earth's magnetic field. These photons have energies in the x-ray and gamma-ray region, and to detect them CREST employs an array of inorganic scintillators. The effective detection area using this technique is significantly larger than the actual detector array size, and has the desirable feature of increasing with electron energy, due to the energy dependence of synchrotron radiation intensity. The CREST project has two phases: CREST-1 is a prototype array of 96 BGO and BaF2 crystals designed to validate the technique, and is scheduled for balloon flight in summer 2005. The full detector, CREST-2, will be a long duration instrument based on a 1600 crystal array.