Abstract. SPI is a high spectral resolution gamma-ray telescope on board the ESA mission INTEGRAL (International Gamma Ray Astrophysics Laboratory). It consists of an array of 19 closely packed germanium detectors surrounded by an active anticoincidence shield of BGO. The imaging capabilities of the instrument are obtained with a tungsten coded aperture mask located 1.7 m from the Ge array. The fully coded field-of-view is 16• , the partially coded field of view amounts to 31• , and the angular resolution is 2.5• . The energy range extends from 20 keV to 8 MeV with a typical energy resolution of 2.5 keV at 1.3 MeV. Here we present the general concept of the instrument followed by a brief description of each of the main subsystems. INTEGRAL was successfully launched in October 2002 and SPI is functioning extremely well.

Abstract. We provide first constraints on the morphology of the 511 keV line emission from the galactic centre region on basis of data taken with the spectrometer SPI on the INTEGRAL gamma-ray observatory. The data suggest an azimuthally symmetric galactic bulge component with FWHM of ∼9• with a 2σ uncertainty range covering 6• −18• . The 511 keV line flux in the bulge component amounts to 9.9 +4.7 −2.1 × 10 −4 ph cm −2 s −1 . No evidence for a galactic disk component has been found so far; upper 2σ flux limits in the range (1.4−3.4) × 10 −3 ph cm −2 s −1 have been obtained that depend on the assumed disk morphology. These limits correspond to lower limits on the bulge-to-disk ratio of 0.3−0.6.