- Ben-Ami, Sagi;
- Gal-Yam, Avishay;
- Mazzali, Paolo A;
- Gnat, Orly;
- Modjaz, Maryam;
- Rabinak, Itay;
- Sullivan, Mark;
- Bildsten, Lars;
- Poznanski, Dovi;
- Yaron, Ofer;
- Arcavi, Iair;
- Bloom, Joshua S;
- Horesh, Assaf;
- Kasliwal, Mansi M;
- Kulkarni, Shrinivas R;
- Nugent, Peter E;
- Ofek, Eran O;
- Perley, Daniel;
- Quimby, Robert;
- Xu, Dong
We present our observations of SN 2010mb, a Type Ic supernova (SN) lacking spectroscopic signatures of H and He. SN 2010mb has a slowly declining light curve (LC) (600 days) that cannot be powered by 56Ni/56Co radioactivity, the common energy source for Type Ic SNe. We detect signatures of interaction with hydrogen-free circumstellar material including a blue quasi-continuum and, uniquely, narrow oxygen emission lines that require high densities (109 cm-3). From the observed spectra and LC, we estimate that the amount of material involved in the interaction was 3 M . Our observations are in agreement with models of pulsational pair-instability SNe described in the literature. © 2014. The American Astronomical Society. All rights reserved..