http://arxiv.org/abs/1601.00686
While recent observations provide evidence that super-Chandrasekhar Type Ia supernovae and at least a fraction of normal Type Ia supernovae probably originate from double-degenerate systems, these two subclasses show distinct characteristics observationally. Here we report an intermediate supernova iPTF13asv that may bridge this gap. On the one hand, similar to normal Type Ia supernovae, the over-luminous iPTF13asv follows the empirical relation between the peak magnitude, the lightcurve shape and its intrinsic color, and shows a near-IR secondary maximum like normal supernovae. On the other hand, similar to super-Chandrasekhar events, it has strong UV emission around maximum, low expansion velocities and persistent carbon absorption. We estimate a $^{56}$Ni mass of $0.81^{+0.10}_{-0.18}M_\odot$ and a total ejecta mass of $1.44^{+0.44}_{-0.12}M_\odot$. Despite these similarities, iPTF13asv lacks iron absorption in its early-phase spectra, indicating a stratified ejecta structure with weak mixing. Based on the strong stratification of the ejecta and the similarity to super-Chandrasekhar events, we infer that iPTF13asv probably originates from a double-degenerate system.
Y. Cao, J. Johansson, P. Nugent, et. al.
Wed, 6 Jan 16
14/43
Comments: 11 pages, 14 figures, Submitted to ApJ. Comments are welcome
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