The Development of GRAPE, a Gamma Ray Polarimeter Experiment.

The measurement of hard X-ray polarization in γ-ray bursts (GRBs) would add yet another piece of information in our effort to resolve the true nature of these enigmatic objects. Here we report on the development of a dedicated polarimeter design with a relatively large FoV that is capable of studying hard X-ray polarization (50-300 keV) from GRBs. This compact design, based on the use of a large area position-sensitive PMT (PSPMT), is referred to as GRAPE (Gamma-RAy Polarimeter Experiment). The feature of GRAPE that is especially attractive for studies of GRBs is the significant off-axis polarization response (at angles greater than 60°). For an array of GRAPE modules, current sensitivity estimates give minimum detectable polarization (MDP) levels of a few percent for the brightest GRBs. [ABSTRACT FROM AUTHOR]