Yi-Chi Chang (NTHU); Jeng-Lun Chiu (NTHU); Chien-Ying Yang (NTHU); Che-Yen Chu (NTHU); Hung-Hsiang Liang (NTHU); Hsiang-Kuang Chang (NTHU); Steven E. Boggs (UCSD, UCB); the COSI Collaboration (UCB, LBNL, NTHU, AS, NCU, IRAP)
The Compton Spectrometer and Imager (COSI) is a soft-gamma ray (0.2 - 5 MeV) imager, spectrometer, and polarimeter designed to perform wide-field imaging, high-resolution spectroscopy, and polarization measurements of astrophysical sources from a high-altitude balloon platform. A successful 46-day flight launched from Wanaka, New Zealand, in May 2016 was recently achieved, resulting in various observations of celestial objects. Among them, Centaurus A, one of the closest AGN from the Earth, was observed with the longest exposure time (> 1 Ms) in the soft gamma-ray band, which is the least explored regime throughout the whole electromagnetic band for this well-studied source. The excellent spectral capability of COSI is anticipated to determine the second maximum around 1 MeV, which plays an important role in resolving the emission of (this) AGN. To achieve this goal, confirming the observation result with simulation is crucial. Therefore, we will present a preliminary study to obtain a realistic simulation by considering (1) atmospheric attenuation, (2) payload orientation along the flight track, (3) mass models reflecting the health of detector array, and (4) the cosmic and atmospheric background. A preliminary comparison between the observation and simulation results will then be shown.