Performance of hard X-ray polarimeter for off-axis injection

Introduction The Gamma Ray Burst (GRB) is one of the most important topics in the fields of astrophysics and is the most energetic phenomenon in the universe. However, the radiation mechanism is still unknown in spite of many studies for about 50 years. Recently, it has been reported that the key to the clarification is in the polarization observation for the hard X-rays from GRBs[1]. However, there is no polarimeter sensitive to GRBs. So we are developing hard X-ray polarimeter with wide field of view in use of two kinds of scintillator. Since the hard X rays often enter to the polarimeter from off-axis, the response of the polarimeter for the off-axis must be investigated in detail. So we constructed prototype polarimeter and then injected hard X rays at 80 keV to the prototype polarimeter at BL14A in Photon Factory of KEK. We will report the experimental results and those of computer simulation.