Balloon-borne sub-MeV/MeV gamma-ray observation using a Compton camera with a gaseous TPC and scintillation camera

We have developed a sub-MeV and MeV gamma-ray imaging Compton camera for use in gamma-ray astronomy; it consists of a gaseous time-projection chamber (TPC) to convert the Compton scattering events and a scintillator array to absorb photons. The TPC measures the energy and three-dimensional tracks of Compton-recoil electrons, while the pixel scintillator arrays measure the energy and positions of scattered gamma rays. Therefore, our camera can reconstruct the incident gamma rays, event by event, over a wide field of view of approximately 3 str. We are now developing a Compton camera for a balloon-borne experiment.