SN2012ab: A Peculiar Type IIn Supernova with Aspherical Circumstellar Material


Christopher Bilinski, Steward Observatory, University of Arizona
Nathan Smith, Steward Observatory, University of Arizona
G Grant Williams, MMT Observatory
Paul Smith, Steward Observatory, University of Arizona
WeiKang Zheng, Department of Astronomy, University of California
Melissa L. Graham, Department of Astronomy, University of California
Jon C. Mauerhan, Department of Astronomy, University of California
Jennifer E. Andrews, Steward Observatory, University of Arizona
Alexei V. Filippenko, Department of Astronomy, University of California, Miller Institute for Basic Research in Science, University of California
Carl Akerlof, Department of Physics, University of Michigan
E Chatzopoulos, Department of Physics and Astronomy, Louisiana State University
Jennifer L. Hoffman, Department of Physics & Astronomy, University of Denver
Leah Huk, Department of Physics & Astronomy, University of Denver
Douglas C. Leonard, Department of Astronomy, San Diego State University
G H. Marion, University of Texas
Peter Milne, Steward Observatory, University of Arizona
Robert M. Quimby, Kavli IPMU, The University of Tokyo
Jeffrey M. Silverman, University of Texas
Jozsef Vinkó, University of Texas, Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, Department of Optics and Quantum Electronics, University of Szeged
J Craig Wheeler, University of Texas
Fang Yuan, Department of Physics, University of Michigan, Research School of Astronomy and Astrophysics, Australian National University, ARC Centre of Excellence for All-sky Astrophysics (CAASTRO)

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College of Natual Science and Mathematics, Physics and Astronomy


We present photometry, spectra, and spectropolarimetry of supernova (SN) 2012ab, mostly obtained over the course of ∼300  d after discovery. SN 2012ab was a Type IIn (SN IIn) event discovered near the nucleus of spiral galaxy 2MASXJ12224762+0536247. While its light curve resembles that of SN 1998S, its spectral evolution does not. We see indications of CSM interaction in the strong intermediate-width emission features, the high luminosity (peak at absolute magnitude M = −19.5), and the lack of broad absorption features in the spectrum. The Hα emission undergoes a peculiar transition. At early times it shows a broad blue emission wing out to −14 000 km s−1 and a truncated red wing. Then at late times (>100 d) it shows a truncated blue wing and a very broad red emission wing out to roughly +20 000 km s−1. This late-time broad red wing probably arises in the reverse shock. Spectra also show an asymmetric intermediate-width Hα component with stronger emission on the red side at late times. The evolution of the asymmetric profiles requires a density structure in the distant CSM that is highly aspherical. Our spectropolarimetric data also suggest asphericity with a strong continuum polarization of ∼1–3 per cent and depolarization in the Hα line, indicating asphericity in the CSM at a level comparable to that in other SNe IIn. We estimate a mass-loss rate of M˙=0.050M⊙yr−1" role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; border: 0px; font-variant: inherit; font-stretch: inherit; line-height: normal; font-family: inherit; vertical-align: baseline; display: inline; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative;">M˙=0.050M⊙yr−1M˙=0.050M⊙yr−1 for vpre = 100 km s−1 extending back at least 75 yr prior to the SN. The strong departure from axisymmetry in the CSM of SN 2012ab may suggest that the progenitor was an eccentric binary system undergoing eruptive mass loss.

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