Development of GAmma-ray burst Polarimeter GAP2

Gamma-ray bursts (GRBs) are the most energetic phenomena in the universe. To elucidate the radiation mechanism of the GRBs, we are developing Compton scattering-type polarimeter which will be installed on next generation solar sails. Under the limitation of the weight about 5 kg for the polarimeter, we have optimized the geometry to obtain the best performance. As a result, we recognized from the computer simulation that the minimum detectable polarization (MDP) of the polarimeter is three times better than that of the Gamma-ray burst polarimeter (GAP) launched in 2010. To investigate the performance of the designed polarimeter, we manufactured a prototype model.