Nathan Smith, Jon Mauerhan, Jose Prieto
The recent supernova (SN) 2009ip had pre-SN eruptions followed by a final explosion in 2012. Its pre-SN observations make 2009ip the best observed SN progenitor in history, but the unprecedented data on the pre-SN activity has fueled debate about the nature of the 2012 explosion, whether it was a true SN or some extreme non-terminal event. In principle, both types of events could power shock interaction with circumstellar material (CSM), but here we argue that only a core-collapse SN provides a self-consistent explanation. Previously, we demonstrated that the light curves of SN 2009ip and another Type IIn, SN 2010mc, were nearly identical. Here we expand that comparison to their spectra as well, demonstrating that they are both consistent with known Type IIn events. The late-time spectra of SN 2009ip resemble those of the super-luminous SN 2006tf, and the underlying broad component in SN 2009ip's spectra resembles Type II-P events. The recent claim that the late-time spectrum of SN 2009ip is returning to its progenitor's LBV-like state is not supported by our observations. The presence of broad Ca II emission, in particular, has only been seen in SNe, and we show that SN 2009ip's changing H-alpha equivalent width after explosion matches the behavior typically seen in SNe IIn. We discuss several key facts about SN 2009ip and SN 2010mc that argue strongly in favor of a core-collapse interpretation for the bright 2012 event, which weakens speculation that it was a non-terminal event. The only viable non-terminal alternative to a core-collapse SN (proposed so far) is the pulsational pair instability, which will occur too infrequently to explain the class of SNe IIn in general. Since no convincing evidence to the contrary exists, the case seems quite strong that SN 2009ip was a core-collapse event where most of the emergent luminosity came from CSM interaction (abridged).
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http://arxiv.org/abs/1308.0112
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