Absence of Fast-moving Iron in an Intermediate Type Ia Supernova between Normal and Super-Chandrasekhar

June 2016 • 2016ApJ...823..147C

Authors • Cao, Yi • Johansson, J. • Nugent, Peter E. • Goobar, A. • Nordin, Jakob • Kulkarni, S. R. • Cenko, S. Bradley • Fox, Ori D. • Kasliwal, Mansi M. • Fremling, C. • Amanullah, R. • Hsiao, E. Y. • Perley, D. A. • Bue, Brian D. • Masci, Frank J. • Lee, William H. • Chotard, Nicolas

Abstract • In this paper, we report observations of a peculiar SN Ia iPTF13asv (a.k.a., SN2013cv) from the onset of the explosion to months after its peak. The early-phase spectra of iPTF13asv show an absence of iron absorption, indicating that synthesized iron elements are confined to low-velocity regions of the ejecta, which, in turn, implies a stratified ejecta structure along the line of sight. Our analysis of iPTF13asv’s light curves and spectra shows that it is an intermediate case between normal and super-Chandrasekhar events. On the one hand, its light curve shape (B-band {{Δ }}{m}₁₅=1.03+/- 0.01) and overall spectral features resemble those of normal SNe Ia. On the other hand, its large peak optical and UV luminosity ({M}_B=-19.84 {{mag}}, {M}_{uvm2}=-15.5 {{mag}}) and its low but almost constant Si II velocities of about 10,000 km s^-1 are similar to those in super-Chandrasekhar events, and its persistent carbon signatures in the spectra are weaker than those seen commonly in super-Chandrasekhar events. We estimate a ⁵⁶Ni mass of {0.81}_-0.18^+0.10{M}_⊙ and a total ejecta mass of {1.59}_-0.12^+0.45{M}_⊙. The large ejecta mass of iPTF13asv and its stratified ejecta structure together seemingly favor a double-degenerate origin.

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Frank Masci

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