New readout and data-acquisition system for reducing dead time in the Gamma Ray Compton Telescope

For MeV gamma-ray astronomy, We have developed an electron-tracking Compton camera (ETCC) as a next generation satellite telescope. Our detector consists of a Comptonscattering target and a scattered gamma-ray absorber. The target is a gaseous Time Projection Chamber (TPC), which uses μPIC as the 2-dimensional readout detector, and the absorber is position sensitive scintillation arrays (PSAs). We developed a prototype ETCC and certificated its performance in a groundbased experiment. The prototype ETCC had a sharp PSF of 15 (included 50%, 662 keV) at the ARM of 5 and the SPD of 100. We plan to update the prototype ETCC and observe the electronpositron annihilation line of the galactic center in Australia in early 2018 (SMILE-II+). In the data acquisition (DAQ) system of the prototype ETCC, the dead time is estimated to be 20 % at the trigger rate of 100 Hz in a balloon observation, and the prototype ETCC can work. The SMILE-II+ ETCC can also work at the balloon altitude. On the other hand, in the future observation with the ETCC, that has a larger effective area than the effective area of SMILE-II+ ETCC, the DAQ rate is expected to be 1 kHz. The dead time gets saturation due to sending data via VME bus and common start system in PSA. To overcome the two problem, we develop a new TPC readout board and a PSA readout unit. We create a test model ETCC which have the new TPC readout boards and the new PSA readout units. Although the dead time is 20 % at 30 Hz with a small ETCC in the prototype DAQ system, the dead time is 20 % at 2 kHz in the new system.