BALLOON-BORNE GAMMA-RAY POLARIMETRY

The physical processes postulated to explain the high-energy emission mechanisms of compact astrophysical sources often yield polarised soft gamma rays (X-rays). PoGOLite is a balloon-borne polarimeter operating in the 25-80 keV energy band. The polarisation of incident photons is reconstructed using Compton scattering and photoelectric absorption in an array of phoswich detec-tor cells comprising plastic and BGO scintillators, sur-rounded by a BGO side anticoincidence shield. The po-larimeter is aligned to observation targets using a cus-tom attitude control system. The maiden balloon flight is scheduled for summer 2011 from the Esrange Space Centre with the Crab and Cygnus X-1 as the primary ob-servational targets