SN 2016coi/ASASSN-16fp: an example of residual helium in a typeIc supernova?
Abstract
The optical observations of Ic-4 supernova (SN) 2016coi/ASASSN-16fp, from ∼2 to ∼450 d after explosion, are presented along with analysis of its physical properties. The SN shows the broad lines associated with SNe Ic-3/4 but with a key difference. The early spectra display a strong absorption feature at ∼5400 Å which is not seen in other SNe Ic-3/4 at this epoch. This feature has been attributed to He I in the literature. Spectral modelling of the SN in the early photospheric phase suggests the presence of residual He in a C/O dominated shell. However, the behaviour of the He I lines is unusual when compared with He-rich SNe, showing relatively low velocities and weakening rather than strengthening over time. The SN is found to rise to peak ∼16 d after core-collapse reaching a bolometric luminosity of Lp∼3 × 1042 erg s-1. Spectral models, including the nebular epoch, show that the SN ejected 2.5-4 M⊙ of material, with ∼1.5 M⊙ below 5000 km s-1, and with a kinetic energy of (4.5-7) × 1051 erg. The explosion synthesized ∼0.14 M⊙ of 56Ni. There are significant uncertainties in E(B - V)host and the distance, however, which will affect Lp and MNi. SN 2016coi exploded in a host similar to the Large Magellanic Cloud (LMC) and away from star-forming regions. The properties of the SN and the host-galaxy suggest that the progenitor had MZAMS of 23-28 M⊙ and was stripped almost entirely down to its C/O core at explosion.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- August 2018
- DOI:
- 10.1093/mnras/sty1223
- arXiv:
- arXiv:1709.03593
- Bibcode:
- 2018MNRAS.478.4162P
- Keywords:
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- supernovae: individual- SN2016coi/ASASSN16-fp;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- Accepted for publication in MNRAS. Updated to reflect the published version, minor typographical changes only