60Fe and Massive Stars

Gamma-ray line emission from radioactive decay of ⁶⁰Fe provides constraints on nucleosynthesis in massive stars and supernovae. We detect the γ-ray lines from ⁶⁰Fe decay at 1173 and 1333 keV using three years of data from the spectrometer SPI on board INTEGRAL. The average flux per line is (4.4 ± 0.9) × 10⁻⁵ ph cm⁻² s⁻¹ rad⁻¹ for the inner Galaxy region. Deriving the Galactic ²⁶Al gamma-ray line flux with using the same set of observations and analysis method, we determine the flux ratio of ⁶⁰Fe/²⁶Al gamma-rays as 0.15 ± 0.05. We discuss the implications of these results for the widely-held hypothesis that ⁶⁰Fe is synthesized in core-collapse supernovae, and also for the closely-related question of the precise origin of ²⁶Al in massive stars.