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تسجيل مستخدم جديدSN 2016coi/ASASSN-16fp: An example of residual helium in a type Ic supernova?
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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 $sim 3times10^{42}$ 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.
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