Hubble Space Telescope spectra of the Type Ia supernova SN 2011fe: a tail of low-density, high-velocity material with Z <Z⊙

P. A. Mazzali, M. Sullivan, S. Hachinger, R. S. Ellis, P. E. Nugent, D. A. Howell, A. Gal-Yam, K. Maguire, J. Cooke, R. Thomas, K. Nomoto, E. S. Walker

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Abstract

Hubble Space Telescope spectroscopic observations of the nearby Type Ia supernova (SN Ia) SN 2011fe, taken on 10 epochs from -13.1 to +40.8 d relative to B-band maximum light, and spanning the far-ultraviolet (UV) to the near-infrared (IR) are presented. This spectroscopic coverage makes SN 2011fe the best-studied local SN Ia to date. SN 2011fe is a typical moderately luminous SN Ia with no evidence for dust extinction. Its near-UV spectral properties are representative of a larger sample of local events (Maguire et al.). The near-UV to optical spectra of SN 2011fe are modelled with a Monte Carlo radiative transfer code using the technique of `abundance tomography', constraining the density structure and the abundance stratification in the SN ejecta. SN 2011fe was a relatively weak explosion, with moderate Fe-group yields. The density structures of the classical model W7 and of a delayed detonation model were tested. Both have shortcomings. An ad hoc density distribution was developed which yields improved fits and is characterized by a high-velocity tail, which is absent in W7. However, this tail contains less mass than delayed detonation models. This improved model has a lower energy than one-dimensional explosion models matching typical SNe Ia (e.g. W7, WDD1; Iwamoto et al.). The derived Fe abundance in the outermost layer is consistent with the metallicity at the SN explosion site in M101 (˜0.5 Z⊙). The spectroscopic rise-time (˜19 d) is significantly longer than that measured from the early optical light curve, implying a `dark phase' of ˜1 d. A longer rise-time has significant implications when deducing the properties of the white dwarf and binary system from the early photometric behaviour.
Original languageEnglish
Pages (from-to)1959-1979
Number of pages21
JournalMonthly Notices of the Royal Astronomical Society
Volume439
Issue number2
Early online date17 Feb 2014
DOIs
Publication statusPublished - 01 Apr 2014
Externally publishedYes

Keywords

  • radiative transfer
  • techniques: spectroscopic
  • supernovae: general
  • supernovae: individual: SN 2011fe

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