POLAR: The first dedicated gamma-ray burst polarization experiment

POLAR is a Gamma-Ray Burst (GRB) polarization experiment in the energy range 50-500 keV. Detection principle of the gamma-ray polarization is based on the anisotropy of the Compton scattering. POLAR consists of 1600 low-Z plastic scintillator bars, read out by 25 flat-panel multianode photomultipliers. Simulations and experiments have shown that the polarization degree and angle can be retrieved from the modulation curves with the required accuracy. POLAR can reach a minimum detectable polarization of about 10%(3-sigma level) for several strongest GRB detections per year. Construction and assembly of the Qualification Model (QM) are ongoing, in view of a flight onboard of the Chinese Spacelab TG-2 scheduled for 2014.