Iron, Cobalt, and Nickel in SN 1987A

Abstract

During the first several weeks after the explosion of SN 1987A, Fe/Co/Ni clumps, containing approx. 1% of the mass of the supernova envelope, absorbed most of the energy release by Ni-56 and Co-56 decay. As a result, the clumps expanded relative to the substrate, forming a 'nickel bubble' of low-density Fe/Co/Ni. Later the clumps captured approx. 10% of the radioactive luminosity of gamma rays and positrons. Assuming that these elements are not mixed microscopically with other elements, we find that the clumps must occupy approx. greater than 30% of the volume of the emitting region (radial velocity approx. less than 2500 km/s). The result indicates that the emission at late times is dominated by an extra source of heating and ionization, most likely photoionization by two-photon continuum from metastable helium in the gas surrounding the clumps. The resulting 'frothy' structure, consisting of bubbles of low-density Fe surrounded by higher-density filaments of H, He, and other elements, will persist and may be seen in the spectra and structure of supernova remnants.