Abstract
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 H-poor SNe and superluminous 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 superluminous 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.
Highlights
Recent transient surveys and growing support from amateur observers have uncovered ever-increasing diversity in the observational properties of supernovae (SNe)
SN 2012au is located at coordinates α = 12h54m52s.18 and δ = −10◦14′50′.′2 (J2000.0), which is is less than 600 pc away in projection from the center of NGC 4790’s bright central nucleus
We have shown that SN 2012au is an energetic (EK ∼ 1052 erg) explosion having a rarely observed combination of late-time properties that suggest a link between subsets of energetic and H-poor SNe and superluminous SNe (SLSNe)
Summary
Recent transient surveys (e.g., the Panoramic Survey Telescope and Rapid Response System, the Palomar Transient Factory, the Catalina Real-Time Transient Survey [CRTS], the Texas Supernova Search operating as the ROTSE Supernova Verification Project) and growing support from amateur observers have uncovered ever-increasing diversity in the observational properties of supernovae (SNe). Some of the more luminous H- and He-poor SNe discovered by these efforts have garnered especial attention because of their connection with long-duration gammaray bursts Superluminous SNe (SLSNe) with absolute magnitudes of −21 are recent members of the growing SN classification zoo (Quimby et al 2011). Hpoor examples can be even more powerful than SNe Ic (Gal-Yam 2012), and there has been considerable effort to understand their nature and relationship with more typical SNe. One of the first examples of the H-poor variety was SN 2007bi (Gal-Yam et al 2009; Young et al 2010), which was originally suggested to be the result of the pair-instability explosion mechanism (Barkat et al 1967). No SLSN has been observationally connected to a GRB
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