Abstract
Recent observations of the Galactic center region by the GRIS balloon-borne germanium spectrometer have determined that the diffuse 1809 keV emission resulting from the decay of 26Al has an intrinsic width of 5.4 keV FWHM. This line width indicates that the 26Al either is at a temperature of ~4.5 × 108 K or has a nonthermal velocity of ~500 km s-1. Previous authors have suggested that the 26Al must be trapped within dust grains in the interstellar medium (ISM) in order for these conditions to persist over the 106 yr lifetime of the aluminum. We discuss the results of our model, in which 26Al dust grains are produced in Type II supernovae and are subsequently reaccelerated in the ISM by ambient supernova remnant (SNR) shocks. Our results show that dust grains can be maintained at a velocity sufficient to explain the GRIS observation for ISM densities of ~0.2 cm-3, dust-grain sizes near 10-5 cm, and distances between SNR shocks in the ISM of 100-200 pc.
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