SN 2008iy: An unusual Type IIn Supernova with an enduring 400-d rise time

A. A. Miller*, J. M. Silverman, N. R. Butler, J. S. Bloom, R. Chornock, A. V. Filippenko, M. Ganeshalingam, C. R. Klein, W. Li, P. E. Nugent, N. Smith, T. N. Steele

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

42 Scopus citations

Abstract

We present spectroscopic and photometric observations of the Type IIn supernova (SN) 2008iy. SN 2008iy showed an unprecedentedly long rise time of ~400 d, making it the first known SN to take significantly longer than 100 d to reach peak optical luminosity. The peak absolute magnitude of SN 2008iy was Mr ≈ -19.1 mag, and the total radiated energy over the first ~700 d was ~2 × 1050 erg. Spectroscopically, SN 2008iy is very similar to the Type IIn SN 1988Z at late times and, like SN 1988Z, it is a luminous X-ray source (both SNe had an X-ray luminosity LX > 1041 erg s-1). SN 2008iy has a growing near-infrared excess at late times similar to several other SNe IIn. The Hα emission-line profile of SN 2008iy shows a narrow P Cygni absorption component, implying a pre-SN wind speed of ~100 km s-1. We argue that the luminosity of SN 2008iy is powered via the interaction of the SN ejecta with a dense, clumpy circumstellar medium. The ~400-d rise time can be understood if the number density of clumps increases with distance over a radius ~1.7 × 1016 cm from the progenitor. This scenario is possible if the progenitor experienced an episodic phase of enhanced mass loss <1 century prior to explosion or if the progenitor wind speed increased during the decades before core collapse. We favour the former scenario, which is reminiscent of the eruptive mass-loss episodes observed for luminous blue variable (LBV) stars. The progenitor wind speed and increased mass-loss rates serve as further evidence that at least some, and perhaps all, Type IIn SNe experience LBV-like eruptions shortly before core collapse.We also discuss the host galaxy of SN 2008iy, a subluminous dwarf galaxy, and offer a few reasons why the recent suggestion that unusual, luminous SNe preferentially occur in dwarf galaxies may be the result of observational biases.

Original languageEnglish (US)
Pages (from-to)305-317
Number of pages13
JournalMonthly Notices of the Royal Astronomical Society
Volume404
Issue number1
DOIs
StatePublished - May 2010
Externally publishedYes

Keywords

  • Circumstellar matter
  • General
  • Individual
  • Mass-loss
  • SN 1988Z
  • SN 2008iy
  • Stars
  • Supernovae

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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