Imaging the 511 keV positron annihilation sky with COSI

Thomas Siegert, Steven E. Boggs, John A. Tomsick +10

The balloon-borne Compton Spectrometer and Imager (COSI) had a successful 46-day flight in 2016. The instrument is sensitive to photons in the energy range $0.2$-$5$ MeV. Compton t…