Measuring nickel masses in Type Ia supernovae using cobalt emission in nebular phase spectra
2015 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 454, no 4, 3816-3842 p.Article in journal (Refereed) PublishedText
The light curves of Type Ia supernovae (SNe Ia) are powered by the radioactive decay of Ni-56 to Co-56 at early times, and the decay of Co-56 to Fe-56 from similar to 60 d after explosion. We examine the evolution of the [Co III] lambda 5893 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 Co-56 as a function of time. This result indicates both efficient local energy deposition from positrons produced in Co-56 decay and long-term stability of the ionization state of the nebula. We compile SN Ia nebular spectra from the literature and present 21 new late-phase spectra of 7 SNe Ia, including SN 2014J. From these we measure the flux in the [Co III] lambda 5893 line and remove its well-behaved time dependence to infer the initial mass of Ni-56 (M-Ni, produced in the explosion. We then examine Ni-56 yields for different SN Ia ejected masses (M-ej-calculated using the relation between light-curve width and ejected mass) and find that the Ni-56 masses of SNe Ia fall into two regimes: for narrow light curves (low stretch s similar to 0.7-0.9), M-Ni is clustered near MN, 0.4 Me and shows a shallow increase as Mei increases from similar to 1 to 1.4 M-circle dot; at high stretch, M-ej clusters at the Chandrasekhar mass (1.4 M-circle dot) while M-Ni, spans a broad range from 0.6 to 1.2 M-circle dot. This could constitute evidence for two distinct SN Ia explosion mechanisms.
Place, publisher, year, edition, pages
2015. Vol. 454, no 4, 3816-3842 p.
Astronomy, Astrophysics and Cosmology
Research subject Astronomy
IdentifiersURN: urn:nbn:se:su:diva-124817DOI: 10.1093/mnras/stv2173ISI: 000368001600041OAI: oai:DiVA.org:su-124817DiVA: diva2:890724