该研究详细描述了Type Ib SN PTF13bvn的光谱偏振观测，发现恒星照片层的非球形性达10%，并追踪了CaIIIR3、HeI/NaID等元素的线偏振。研究者推测高速Hα吸收特征，并揭示了双线形成区域的存在。通过HeIλ5876的偏振特性，推断放射性镍主要位于外壳内。文章还讨论了可能的前身系统，倾向于爆炸源自带有扭曲外层的较大恒星而非紧凑的WR星。
摘要：
We present six epochs of spectropolarimetric observations and one epoch of spectroscopy of the Type Ib SN iPTF 13bvn. The epochs of these observations correspond to $-$10 to $+$61 days with respect to the {\it r}-band light curve maximum. The continuum is intrinsically polarised to the $0.2-0.4\%$ level throughout the observations, implying asphericities of $\sim10\%$ in the shape of the photosphere. We observe significant line polarisation associated with the spectral features of Ca II IR3, He I/Na I D, He I {\lambda}{\lambda}6678, 7065, Fe II {\lambda}4924 and O I {\lambda}7774. We propose that an absorption feature at $\sim 6200\mathrm{\AA}$, usually identified as Si II $\lambda 6355$, is most likely to be high velocity $\mathrm{H\alpha}$ at $-16,400$ $\mathrm{km \; s^{-1}}$. Two distinctly polarised components, separated in velocity, are detected for both He I/Na I D and Ca II IR3, indicating the presence of two discrete line forming regions in the ejecta in both radial velocity space and in the plane of the sky. We use the polarisation of He I $\lambda 5876$ as a tracer of sources of non-thermal excitation in the ejecta; finding that the bulk of the radioactive nickel was constrained to lie interior to $\sim 50-65\%$ of the ejecta radius. The observed polarisation is also discussed in the context of the possible progenitor system of iPTF 13bvn, with our observations favouring the explosion of a star with an extended, distorted envelope rather than a compact Wolf-Rayet star.
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