Presentation #406.01 in the session Exploring the MeV Gamma-ray Sky: The Past, Present, and Future.
The spectrometer onboard the International Gamma-Ray Astrophysics Laboratory (INTEGRAL/SPI) is measuring photons between 0.02 and 8 MeV since 2002 and will be operational until the end of 2024. With its high purity germanium detectors, its coded aperture mask, and thanks to more than two decades in space, SPI is the currently most sensitive high-resolution gamma-ray spectrometer telescope. The science SPI is enabling is diverse and includes many astrophysical objects. The targets range from gamma-ray line spectroscopy of point sources, over Galactic diffuse emission in continuum and lines, to transients like gamma-ray bursts and solar flares. Despite its age, data analysis techniques for SPI are continuously improved so that even now, its scientific return is enormous. In this talk I will explain how the coded aperture mask works and highlight the observational achievements that were only made possible by measurements with SPI. Among these highlights are the 511 keV line from electron-positron annihilation, the diffuse emission from short-lived isotopes and relativistic electrons, as well as the ability to constrain dark matter properties by Galactic and extragalactic observations.