SN 2016coi/ASASSN-16fp: An example of residual helium in a type Ic supernova?

• Published in: arXiv.org 2018-05
• Main Authors: Prentice, S J, Ashall, C, Mazzali, P A, J -J Zhang, James, P A, X -F Wang, Vinko, J, Percival, S, Short, L, Piascik, A, Huang, F, J Mo, L -M Rui, J -G Wang, D -F Xiang, Xin, Y -X, W -M Yi, X -G Yu, Zhai, Q, T -M Zhang, Hosseinzadeh, G, Howell, D A, McCully, C, Valenti, S, Cseh, B, Hanyecz, O, Kriskovics, L, Pal, A, Sarneczky, K, Sodor, A, Szakats, R, Szekely, P, Varga-Verebelyi, E, Vida, K, Bradac, M, Reichart, D E, Sand, D, Tartaglia, L
• Format: Article
• Language: English
• Subjects: Bolometers; Collapse; Explosions; Galaxies; Helium; Kinetic energy; Luminosity; Magellanic clouds; Nebulae; Photosphere; Physical properties; Spectra; Star formation
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1709.03593

The optical observations of Ic-4 supernova (SN) 2016coi/ASASSN-16fp, from \(\sim 2\) to \(\sim450\) days 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 \(\sim 5400\) \AA\ 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 are 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 \(\sim 16\) d after core-collapse reaching a bolometric luminosity of Lp \(\sim 3\times10^{42}\) \ergs. Spectral models, including the nebular epoch, show that the SN ejected \(2.5-4\) \msun\ of material, with \(\sim 1.5\) \msun\ below 5000 \kms, and with a kinetic energy of \((4.5-7)\times10^{51}\) erg. The explosion synthesised \(\sim 0.14\) \msun\ 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 \(M_\mathrm{ZAMS}\) of \(23-28\) \msun\ and was stripped almost entirely down to its C/O core at explosion.