2015/07/06 by Michael J. Childress, D. John Hillier, Ivo Seitenzahl +34 · 2 citations
Physics and Astronomy · #astro-ph.HE #astro-ph.SR
paper · pdf · doi:10.1093/mnras/stv2173
16 pages, 12 figures (main text), plus data tables in appendix. Spectra released on WISeREP. Submitted to MNRAS, comments welcome
arxiv created 2015/07/06 · arxiv updated 2015/11/04
The light curves of Type Ia supernovae (SNe Ia) are powered by the radioactive decay of 56Ni to 56Co at early times, and the decay of 56Co to 56Fe from ~60 days after explosion. We examine the evolution of the [Co III] 5892 A emission complex during the nebular phase for SNe Ia with multiple nebular spectra and show that the line flux follows the square of the mass of 56Co as a function of time. This result indicates both efficient local energy deposition from positrons produced in 56Co decay, and long-term stability of the ionization state of the nebula. We compile 77 nebular spectra of 25 SN Ia from the literature and present 17 new nebular spectra of 7 SNe Ia, including SN2014J. From these we measure the flux in the [Co III] 5892 A line and remove its well-behaved time dependence to infer the initial mass of 56Ni (MNi) produced in the explosion. We then examine 56Ni yields for different SN Ia ejected masses (Mej - calculated using the relation between light curve width and ejected mass) and find the 56Ni masses of SNe Ia fall into two regimes: for narrow light curves (low stretch s~0.7-0.9), MNi is clustered near MNi ~ 0.4M_\odot and shows a shallow increase as Mej increases from ~1-1.4M_\odot; at high stretch, Mej clusters at the Chandrasekhar mass (1.4M_\odot) while MNi spans a broad range from 0.6-1.2M_\odot. This could constitute evidence for two distinct SN Ia explosion mechanisms.