Systematic Study of Nuclear Gamma-Ray Spectra of One Hundred Super Novae Expected by Future Nuclear Gamma-Ray Imaging Spectroscopic Observations

Supernovae (SNe) are the most fascinating objects in astronomy and are intensely investigated. However, many mysteries such as nucleosynthesis and the origin of SNe Ia remain unsolved. Although the thermonuclear explosion of a single-degenerate white dwarf has been considered to be the origin of SNe Ia, a merger of two white dwarfs (double-degenerate scenario) has been frequently denoted to be more promising than a single-degenerate white dwarf. Recently the importance of observing the MeV gamma-ray band to conclusively determine the origin has been remarked. MeV gamma-rays are unique probes directly emitted from the exploding or merging region. It is evident that statistical analysis based on imaging spectroscopic observations of ~100 SNe Ia with MeV gamma-rays is necessary to obtain a definite answer. To achieve this, a telescope with a sensitivity that is 100 times that of COMPTEL is necessary. Proper imaging spectroscopy for the MeV gamma-ray band has been established by an electron-tracking Compton camera; hence, a concrete design of a MeV gamma-ray telescope has been proposed in our previous work. We have studied the details of the spectroscopic feature of SNe Ia based on the performance of a proposed telescope and found that statistical analysis can considerably suppress fluctuations of the individual properties of SNe and reveal their intrinsic differences in averaged light curves of SNe up to 60 Mpc. Our answer for the origin of SNe Ia extends to the case of single-degenerate scenario and double-degenerate coexistence scenario.