2016ApJ...823..147C

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}_{{uvm}2}=-15.5 mag ) and its low but almost constant Si ii velocities of about 10,000 km/s 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.