http://arxiv.org/abs/1502.00646
We present a “kiloday” optical nebular spectrum of the nearby Type Ia supernova (SN) 2011fe, obtained +981 days after explosion. SN 2011fe exhibits little evolution since the +593 day optical spectrum, but there are several curious aspects in this new extremely late-time regime. We see new emission features at 5800 and 6400 \AA\ that could be attributed to [Fe I], but also consider (and reject) the possibility that the latter is the high-velocity hydrogen predicted by Mazzali et al. (2014). The nebular feature at 5200 \AA\ exhibits a linear velocity evolution of $\sim350$ $\rm km\ s^{-1}$ per 100 days from at least +220 to +980 days, but the line’s shape also changes in this time, suggesting that line blending contributes to the evolution. At $\sim 1000$ days after explosion, flux from the SN has declined to a point where contribution from a hot, luminous secondary could be detected. In this work we make the first observational tests for a post-impact remnant star and constrain its luminosity to $<(3-5) \times 10^3$ $\rm L_{\odot}$. Additionally, we do not see any evidence for narrow H$\alpha$ emission, placing an upper limit of $3 \times 10^{-4}$ $\rm M_{\odot}$ on the mass of hydrogen in the system. We conclude that observations continue to strongly exclude many single-degenerate scenarios for SN 2011fe.
M. Graham, P. Nugent, M. Sullivan, et. al.
Wed, 4 Feb 15
25/59
Comments: 10 pages, 10 figures, submitted to MNRAS
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