26Al studies with integral's spectrometer SPI

Al-26 radioactivity traces recent nucleosynthesis throughout the Galaxy, and is known to be produced in massive stars and novae. The map from its decay gamma-ray line suggests massive stars to dominate, but high-resolution line spectroscopy is expected to supplement imaging of Al-26 source regions and thus to help decide about the Al-26 injection process and interstellar environment, hence about the specific massive-star subgroup and phase which produces interstellar Al-26. The INTEGRAL Spectrometer SPI has observed Galactic Al-26 radioactivity in its 1809 keV gamma-ray line during its first inner-Galaxy survey. Instrumental background lilies make analysis difficult; yet, a clear signal from the inner Galaxy agrees with expectations. In particular, SPI has constrained the line width to exclude previously-reported line broadenings corresponding to velocities > 500 km s(-1). The signal-to-background ratio of similar or equal to percent implies that detector response and background modeling need to be fine-tuned to eventually enable line shape deconvolution in order to extract source location information along the line of sight.