Polarimetry with the Soft Gamma-ray Detector onboard Hitomi

Hirokazu Odaka

Polarimetry in the X-ray and gamma-ray bands is still considered to be technically very challenging. The Soft Gamma-ray Detector (SGD) onboard Hitomi is a collimation-type detector covering an energy range of 50-600 keV. Since this instrument consists of semiconductor Compton cameras, it also has capability to measure polarization. The design of the SGD enables precise reconstruction of Compton scattering events inside the instrument, which is essential not only for Compton spectroscopic imaging but also for reliable polarimetry. A ground test at a synchrotron photon beam facility SPring-8 has shown its excellent polarimetric performance by using an engineering model of the SGD, which has a structure completely identical to that of the Compton camera flight model. Due to the regretful loss of the satellite about a month after its launch, we could not conduct most of our observation plans. However, the SGD had worked well until the incident, and brought us interesting data. In this talk, we will present very initial results obtained with the SGD and will discuss the polarization measurement in the hard X-ray and soft gamma-ray bands.