http://arxiv.org/abs/2009.14215
SN2017hcc was remarkable for being a nearby and strongly polarized superluminous TypeIIn supernova (SN). We obtained high-resolution echelle spectra that we combine with other spectra to investigate its line profile evolution. All epochs reveal narrow P~Cygni components from pre-shock circumstellar material (CSM), indicating an axisymmetric outflow from the progenitor of 40-50 km/s. Intermediate-width and broad components exhibit the classic evolution seen in luminous SNe~IIn: symmetric Lorentzian profiles from pre-shock CSM lines broadened by electron scattering at early times, transitioning at late times to multi-component, irregular profiles coming from the SN ejecta and post-shock shell. As in many SNe~IIn, profiles show a progressively increasing blueshift, with a clear flux deficit in red wings of the intermediate and broad velocity components after day 200. This blueshift develops after the continuum luminosity fades, and in the intermediate-width component, persists at late times even after the SN ejecta fade. In SN2017hcc, the blueshift cannot be explained as occultation by the SN photosphere, pre-shock acceleration of CSM, or a lopsided explosion or CSM. Instead, the blueshift arises from dust formation in the post-shock shell and in the SN ejecta. The effect has a wavelength dependence characteristic of dust, exhibiting an extinction law consistent with large grains. Thus, SN2017hcc experienced post-shock dust formation and had a mildly bipolar CSM shell, similar to SN2010jl. Like other superluminous SNeIIn, the progenitor lost around 10Msun due to extreme eruptive mass loss in the decade before exploding.
N. Smith and J. Andrews
Thu, 1 Oct 20
67/74
Comments: 21 pages, 16 figures, accepted in MNRAS
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