Nuclear astrophysics with gamma-ray line observations

Abstract

Gamma-ray spectrometers with high spectral resolution have been operated in space since 2002. Major efforts to understand instrumental response and backgrounds are a requird before detailed science interpretations can be derived; by now, high-resolution line-shape studies have resulted in significant astrophysical constraints, not only through studies of solar-flare details, but also for nuclear processes in the Galaxy: 44 Ti from the Cas A supernova could only be detected in the low-energy lines at 68 and 78 keV, the 1157 keV line from the same decay is not seen; this constrains 44 Ti ejection in core collapse supernovae. Diffuse nucleosynthesis is studied through 26 Al, 60 Fe, and positron annihilation gamma-ray measurements. The gamma-ray line from decay of radioactive 26 Al could be measured at unpredecented spectroscopic precision. The new determination of the total mass of 26 Al produced by stellar sources throughout the Galaxy yields 2.8 ±0.9 M , and the interstellar medium around 26 Al sources appears characterized by velocities in the ~100 km s -1 region. 60 Fe is clearly detected with SPI, its intensity ratio to 26 Al of ~15% is on the lower side of predictions from massive-star and supernova nucleosynthesis models. Nucleosynthesis sources are probably minor contributors to Galactic positrons; this may be deduced from the bulge-centered spatial distribution of the annihilation gamma-ray emission, considering that nucleosynthesis sources are expected to populate mainly the disk part of the Galaxy. It is evident that new views at nuclear and astrophysical processes in and around cosmic sources are being provided through these space missions.