D. Milisavljevic, A. Soderberg, R. Margutti, M. Drout, G. Marion, N. Sanders, E. Hsiao, R. Lunnan, R. Chornock, R. Fesen, J. Parrent, E. Levesque, E. Berger, R. Foley, P. Challis, R. Kirshner, J. Dittmann, A. Bieryla, A. Kamble, S. Chakroborti, G. De Rosa, M. Fausnaugh, K. Hainline, C. Chen, R. Hickox, N. Morrell, M. Phillips, M. Stritzinger
We present optical and near-infrared observations of SN 2012au, a slow-evolving supernova (SN) with properties that suggest a link between subsets of energetic and super-luminous SNe. SN 2012au exhibited conspicuous SN Ib-like He I lines and other absorption features at velocities reaching 2 x 10^4 km/s in its early spectra, and a broad light curve that peaked at M_B = -18.1 mag. Models of these data indicate a large explosion kinetic energy of 10^{52} erg and 56Ni mass ejection of 0.3 Msolar on par with SN 1998bw. SN 2012au's spectra almost one year after explosion show a blend of persistent Fe II P-Cyg absorptions and nebular emissions originating from two distinct velocity regions. These late-time emissions include strong [Fe II], [Ca II], [O I], Mg I], and Na I lines at velocities > 4500 km/s, as well as O I and Mg I lines at noticeably smaller velocities of 2000 km/s. Many of the late-time properties of SN 2012au are similar to the slow-evolving hypernovae SN 1997dq and SN 1997ef, and the super-luminous SN 2007bi. Our observations suggest that a single explosion mechanism may unify all of these events that span -21 < M_B < -17 mag. The aspherical and possibly jetted explosion was most likely initiated by the core collapse of a massive progenitor star, and created substantial high-density, low-velocity Ni-rich material.
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http://arxiv.org/abs/1304.0095
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