极亮Ia型超新星2009 dc的分光偏振测量：超巨拉塞卡质量白矮星的近球形爆炸
Spectropolarimetry of Extremely Luminous Type Ia Supernova 2009dc: Nearly Spherical Explosion of Super-Chandrasekhar Mass White Dwarf
摘要：
本文介绍了对一颗Ia型超新星SN 2009 dc的首次偏振光谱观测。在B带最大值后5.6天和89.5天进行观察。在较晚的时期所采取的数据被用来确定星际偏振。连续极化被发现是小的（<0.3%），表明爆炸是近球对称的。这一事实表明SN 2009 dc不太可能发生非球面爆炸。在Si II和Ca II线的极化清楚地显示了Q-U平面中的一个环，表明中间质量元素的非轴对称，clusional分布。在Si和Ca线上的线极化程度是中等的（分别为0.5% ± 0.1%和0.7% ± 0.1%），但它高于从其他Ia型SNe的趋势所预期的。这可能表明，在厚的富56 Ni层（>~ 1.2 Msun）上方存在足够厚的富硅层。观测到的光谱偏振特性，结合光度和光谱特性，表明SN 2009 dc的前身具有超克拉塞卡质量，爆炸几何形状是全球球对称的，中等质量元素呈团块状分布。
英文摘要：
We present the first spectropolarimetric observations of a candidate of super-Chandrasekhar mass Type Ia supernova (SN): SN 2009dc. The observations were performed at 5.6 and 89.5 days after the B-band maximum. The data taken at the later epoch are used to determine the interstellar polarization. Continuum polarization is found to be small (<0.3 %), indicating that the explosion is nearly spherically symmetric. This fact suggests that a very aspherical explosion is not a likely scenario for SN 2009dc. Polarization at the Si II and Ca II lines clearly shows a loop in the Q-U plane, indicating a non-axisymmetric, clumpy distribution of intermediate-mass elements. The degree of line polarization at the Si and Ca line is moderate (0.5% +- 0.1% and 0.7% +- 0.1%, respectively), but it is higher than expected from the trend of other Type Ia SNe. This may suggest that there are thick enough, clumpy Si-rich layers above the thick 56Ni-rich layers (>~ 1.2 Msun). The observed spectropolarimetric properties, combined with the photometric and spectroscopic properties, suggest that the progenitor of SN 2009dc has a super-Chandrasekhar mass, and that the explosion geometry is globally spherically symmetric, with clumpy distribution of intermediate-mass elements.
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