Nickel Mixing in the Outer Layers of SN 1987A

Abstract

Supernova 1987A remains the most well-observed and well-studied supernova to date. Observations produced excellent broad-band photometric and spectroscopic coverage over a wide wavelength range at all epochs. Here, we focus on the very early spectroscopic observations. Only recently have numerical models been of sufficient detail to accurately explain the observed spectra. In SN 1987A, good agreement has been found between observed and synthetic spectra for day one, but by day four, the predicted Balmer lines become much weaker than the observed lines. We present the results of work based on a radiation-hydrodynamic model by Blinnikov and collaborators. Synthetic non-LTE spectra generated from this model by the general radiation transfer code PHOENIX strongly support the theory that significant mixing of nickel into the outer envelope is required to maintain strong Balmer lines. Preliminary results suggest a lower limit to the average nickel mass of 1.0 \times 10^{-5} solar masses is required above 5000 \kmps by day four. PHOENIX models thus have the potential to be a sensitive probe for nickel mixing in the outer layers of a supernova.