Basic Performance of a Polarimeter for Gamma-Ray Bursts Using Segmented Scintillators

We have been developing a Compton-scattering-type hard-X-ray polarimeter sensitive over the energy range from ~ 60 keV to ~ 300 keV for Gamma-Ray Burst (GRB) studies. The polarimeter consists of four identical modules each with a field of view of ±45°. To estimate the instrument performance accurately, we have investigated the instrument's response for gamma rays incident off-axis. We report here results of computer simulations coupled with basic experiments using polarized X-ray beams. As a result of this work we estimate that our polarimeter can detect the polarization for ~ 100 GRBs in 5 years at 99% confidence level if the degree of polarization is higher than 40%.