From balloon to satellite: Measuring Galactic 26Al with the Compton Spectrometer and Imager

The Compton Spectrometer and Imager (COSI) is a 0.2-5 MeV Compton telescope designed for spectroscopy, imaging, and polarimetry. Like INTEGRAL SPI, the heart of COSI is comprised of high-purity germanium detectors with excellent energy resolution. COSI was originally developed as a balloon-borne instrument which flew for 46-days on a NASA superpressure balloon in 2016. The flight was a scientific and technological success: COSI detected and imaged the Galactic positron-electron annihilation excess at 511 keV, detected and placed an upper limit on the polarization of GRB160530A, detected the Crab nebula, and in a recent analysis, measured the 1809 keV decay signature of radioactive Galactic Al-26 with 3.7σ significance. The Inner Galaxy flux of Al-26 is reported as (8.6 +- 2.5) x 10-4 ph/cm2/s. This presentation will detail the Al-26 analysis, compare results to those from SPI, and outline the expected performance of COSI as a NASA Small Explorer satellite mission, slated for launch in 2027.