Gamma-ray lines from SN1987A

Abstract

Gamma-ray spectroscopy of SN1987A has provided us for the first time with a direct confirmation of the existence of explosive nucleosynthesis. Characteristic lines from the decay of radioactive 56Ni have been detected by both balloon and satellite-borne experiments. Lines at 847, 1238 and 2599 keV from excited levels of 56Fe (the final decay product of 56Ni) have been observed. Spherically symmetric, homogeneous models of SN1987A have been quite successful at providing a self-consistent explanation of the gamma-ray line intensity as a function of time. They have not, however, been successful at explaining the line profiles. The measured line profiles suggest the presence of red-shifts whereas the models predict blue shifts. Furthermore, the measured gamma-ray line widths, are characteristically a factor of two greater than the model predictions. The gamma-ray line profiles suggest that we are seeing a significant portion of the receding material on the back side of the shell. These lines are typically optically thick. To explain this apparent contradiction, it may be necessary to invoke fragmentation or non-spherical geometries.