Using late-time optical and near-infrared spectra to constrain Type Ia supernova explosion properties

K. Maguire, S. A. Sim, L. Shingles, J. Spyromilio, A. Jerkstrand, M. Sullivan, T. -W. Chen, R. Cartier, G. Dimitriadis, C. Frohmaier, L. Galbany, C. P. Gutiérrez, G. Hosseinzadeh, D. A. Howell, C. Inserra, R. Rudy, J. Sollerman

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Abstract

The late-time spectra of Type Ia supernovae (SNe Ia) are powerful probes ofthe underlying physics of their explosions. We investigate the late-timeoptical and near-infrared spectra of seven SNe Ia obtained at the VLT withXShooter at >200 d after explosion. At these epochs, the inner Fe-rich ejectacan be studied. We use a line-fitting analysis to determine the relative linefluxes, velocity shifts, and line widths of prominent features contributing tothe spectra ([Fe II], [Ni II], and [Co III]). By focussing on [Fe II] and [NiII] emission lines in the ~7000-7500 \AA\ region of the spectrum, we find thatthe ratio of stable [Ni II] to mainly radioactively-produced [Fe II] for mostSNe Ia in the sample is consistent with Chandrasekhar-mass delayed-detonationexplosion models, as well as sub-Chandrasekhar mass explosions that havemetallicity values above solar. The mean measured Ni/Fe abundance of our sampleis consistent with the solar value. The more highly ionised [Co III] emissionlines are found to be more centrally located in the ejecta and have broaderlines than the [Fe II] and [Ni II] features. Our analysis also strengthensprevious results that SNe Ia with higher Si II velocities at maximum lightpreferentially display blueshifted [Fe II] 7155 \AA\ lines at late times. Ourcombined results lead us to speculate that the majority of normal SN Iaexplosions produce ejecta distributions that deviate significantly fromspherical symmetry.
Original languageEnglish
Number of pages17
JournalMonthly Notices of the Royal Astronomical Society
Early online date30 Mar 2018
DOIs
Publication statusEarly online - 30 Mar 2018

Keywords

  • astro-ph.HE
  • astro-ph.CO
  • astro-ph.SR
  • supernovae: general
  • techniques: spectroscopic
  • line: profiles
  • RCUK
  • STFC
  • ST/M005348/1
  • ST/P000312/1
  • AST-1311862
  • AST-1313484

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