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arXiv · 2111.00016

A Rapid Ionization Change in the Nebular-Phase Spectra of the Type Ia SN 2011fe

M. A. Tucker·C. Ashall·B. J. Shappee·C. S. Kochanek·K. Z. Stanek·P. Garnavich
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Abstract

We present three new spectra of the nearby Type Ia supernova (SN Ia) 2011fe covering $\approx 480-850~$days after maximum light and show that the ejecta undergoes a rapid ionization shift at $\sim 500~$days after explosion. The prominent [FeIII] emission lines at $\approx 4600~$\r{A} are replaced with the permitted FeI+FeII blends at $\sim 4400~$\r{A} and $\sim 5400~$\r{A}. The $\approx 7300~$\r{A} feature, which is produced by [FeII]+[NiII] at $\lesssim 400~$days after explosion, is replaced by broad ($\approx \pm 15\,000~\rm{km}~\rm{s}^{-1}$) symmetric [CaII] emission. Models predict this ionization transition occurring $\sim 100$ days later than what is observed, which we attribute to clumping in the ejecta. Finally, we use the nebular-phase spectra to test several proposed progenitor scenarios for SN2011fe. Non-detections of H and He exclude nearby non-degenerate companions, [OI] non-detections disfavor the violent merger of two white dwarfs, and the symmetric emission-line profiles favor a symmetric explosion.

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M. A. Tucker, C. Ashall, B. J. Shappee, C. S. Kochanek, K. Z. Stanek, P. Garnavich. 2021-10-29. A Rapid Ionization Change in the Nebular-Phase Spectra of the Type Ia SN 2011fe. https://doi.org/10.3847/2041-8213%2Fac4fbd

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