C.-Y. Chu; J.-L. Chiu; C.-Y. Yang; Y.-C. Chang; H.-H. Liang; S. Boggs; H.-K. Chang; P. Jean; for the COSI cooperation
The COmpton Spectrometer and Imager (COSI) is a wide-field gamma ray telescope whose energy range is from 0.2 to 5 MeV. The heart of COSI is a compact array of twelve high-purity cross-strip germanium detectors. The novel detector technique provides COSI a significant improvement of efficiency beyond the former generation of Compton telescope, i.e. CGRO/COMPTEL. COSI performed various ground calibrations before its successful balloon flight in 2016. Study of the effective area calibrations using radioactive sources sampling in the field of view (FoV) determines the actual efficiency of those pointings, with which the comparison of the simulation results extends our efficiency knowledge throughout COSI's FoV, and then helps to determine the flux level of the astrophysical source measured in the 2016 flight. Here, we will report results of this study considering its energy and spatial dependences.