Fermi Gamma-ray Space Telescope

All Sky Survey with an Electron-Tracking Compton and Pair-Tracking Camera using a Gaseous Time Projection Chamber

Atsushi Takada
T. Tanimori, H. Kubo, J. D. Parker, T. Mizumoto, Y. Mizumura, T. Sawano, K. Nakamura, Y. Matsuoka, S. Komura, S. Nakamura, T. Kishimoto, M. Oda, T. Takemura, S. Miyamoto, K. Miuchi, S. Kurosawa


Over ten years from COMPTEL mission, an MeV gamma-ray window does not open, because there is a serious problem which observations are obstructed by a huge background. COMPTEL tried to reject background with time of flight between a scatterer and an absorber, but it was not enough to obtain a designed sensitivity. The unique solution for background suppression is electron-tracking. By the electron-tracking, we can reconstruct Compton-scattering completely. In addition, the electron-tracking provides two independent background-suppression methods: 1) Compton-kinematics test using the angle between scattering direction and recoil direction, and 2) particle identification using the energy deposit rate. Utilizing the advantages of the electron-tracking, we are developing an electron-tracking Compton camera (ETCC) using a gaseous electron tracker. The results of first balloon flight and the experiment in the strong radiation field using a proton beam proved that our ETCC has a powerful background rejetion ability, and it can detect gamma-ray sources with a good signal to noise ratio. If four ETCCs using 50 cm-cubic electron trackers with 3 atm Xe gas loaded on a satellite, the detection sensitivity will reach to 1 mCrab, which is 100 times higher than that of COMPTEL. Moreovre, our ETCC can detect >10 MeV using electron-positron pair tracking with a good angular resolution, so that an ETCC will realize a precise sky survey in multi energy band. In this presentation, we report the performance of the current ETCC and the future plan.