The Unusual Temporal and Spectral Evolution of SN2011ht. II. Peculiar Type IIn or Impostor?
Abstract
SN2011ht has been described both as a true supernova (SN) and as an impostor. In this paper, we conclude that it does not match some basic expectations for a core-collapse event. We discuss SN2011ht's spectral evolution from a hot dense wind to a cool dense wind, followed by the post-plateau appearance of a faster low density wind during a rapid decline in luminosity. We identify a slow dense wind expanding at only 500-600 km s-1, present throughout the eruption. A faster wind speed V ~ 900 km s-1 occurred in a second phase of the outburst. There is no direct or significant evidence for any flow speed above 1000 km s-1 the broad asymmetric wings of Balmer emission lines in the hot wind phase were due to Thomson scattering, not bulk motion. We estimate a mass-loss rate of order 0.05 M ⊙ yr-1 during the hot dense wind phase of the event. The same calculations present difficulties for a hypothetical unseen SN blast wave. There is no evidence that the kinetic energy greatly exceeded the luminous energy, roughly 3 × 1049 erg so the radiative plus kinetic energy was small compared to a typical SN. We suggest that SN2011ht may have been a giant eruption driven by super-Eddington radiation pressure, perhaps beginning a few months before the discovery. A strongly non-spherical SN might also account for the data at the cost of more free parameters.
Based on observations with the Large Binocular Telescope (LBT), an international collaboration among institutions in the United States, Italy, and Germany. LBT Corporation partners are: The University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; The Ohio State University, and The Research Corporation, on behalf of The University of Notre Dame, University of Minnesota, and University of Virginia. Based also on observations obtained at the MMT Observatory, a joint facility of the Smithsonian Institution and the University of Arizona, on data from the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555, and on observations from the Gemini Observatory, operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Science and Technology Facilities Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência e Tecnologia (Brazil), and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina).- Publication:
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The Astrophysical Journal
- Pub Date:
- November 2012
- DOI:
- 10.1088/0004-637X/760/1/93
- arXiv:
- arXiv:1207.5755
- Bibcode:
- 2012ApJ...760...93H
- Keywords:
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- supernovae: individual: SN2011ht;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- To appear in the Astrophysical Journal, Nov. 20 issue. Expanded discussion re SN impostors and Type IIn SNe plus two new figures