对可能的超克拉塞卡质量Ia型超新星2009 dc的十四个月观测
Fourteen Months of Observations of the Possible Super-Chandrasekhar Mass Type Ia Supernova 2009dc
摘要：
本文介绍和分析了一颗极其明亮、演化缓慢的Ia型超新星（SN Ia）2009 dc的光度学和光谱，并提供了它是一颗超克拉塞卡质量（SC）的SN Ia，因而具有SC白矮星（WD）祖先的证据。SN 2007 if是一个类似的天体，它的光谱也被显示出来。SN 2009 dc的光变曲线是SN Ia观测到的最慢的光变曲线之一，上升时间约为23天，Δ m_15（B）= 0.72 mag.我们计算出峰值辐射热光度的下限约为2.4e43 erg/s，尽管实际值可能大了近40%。SN 2009 dc和SN 2007 if在接近最大亮度时获得的光谱表现出很强的C II特征（表明有大量的未燃烧物质），最大亮度后的光谱主要由铁族元素组成。我们所有的SN 2009 dc和SN 2007 if的光谱也显示出低膨胀速度。然而，我们在SN 2009 dc中没有看到像SN 2007 if那样在最大亮度附近出现速度“平台”的强有力证据（Scalzo et al. 2010）。SN 2009 dc的高光度和低膨胀速度使我们得出WD的前身质量可能超过2 M_Sun，Ni-56的质量约为1.4-1.7 M_Sun。我们认为SN 2009 dc的宿主星系在相对较近的过去经历了与邻近星系的引力相互作用。这可能导致了恒星形成的突然爆发，这可能产生了SN 2009 dc的SC WD祖先，并可能将邻近的星系变成了“后星暴星系”。“没有发表的模型似乎与SN 2009 dc中观察到的极端值相匹配，但模拟确实表明，这种大规模的祖先可以存在（可能是两个WD合并的结果），并且可能作为SC SNe Ia爆炸。
英文摘要：
In this paper, we present and analyse optical photometry and spectra of the extremely luminous and slowly evolving Type Ia supernova (SN Ia) 2009dc, and offer evidence that it is a super-Chandrasekhar mass (SC) SN Ia and thus had a SC white dwarf (WD) progenitor. Optical spectra of SN 2007if, a similar object, are also shown. SN 2009dc had one of the most slowly evolving light curves ever observed for a SN Ia, with a rise time of ~23 days and Delta m_15(B) = 0.72 mag. We calculate a lower limit to the peak bolometric luminosity of ~2.4e43 erg/s, though the actual value is likely almost 40% larger. Optical spectra of SN 2009dc and SN 2007if obtained near maximum brightness exhibit strong C II features (indicative of a significant amount of unburned material), and the post-maximum spectra are dominated by iron-group elements. All of our spectra of SN 2009dc and SN 2007if also show low expansion velocities. However, we see no strong evidence in SN 2009dc for a velocity "plateau" near maximum light like the one seen in SN 2007if (Scalzo et al. 2010). The high luminosity and low expansion velocities of SN 2009dc lead us to derive a possible WD progenitor mass of more than 2 M_Sun and a Ni-56 mass of about 1.4-1.7 M_Sun. We propose that the host galaxy of SN 2009dc underwent a gravitational interaction with a neighboring galaxy in the relatively recent past. This may have led to a sudden burst of star formation which could have produced the SC WD progenitor of SN 2009dc and likely turned the neighboring galaxy into a "post-starburst galaxy." No published model seems to match the extreme values observed in SN 2009dc, but simulations do show that such massive progenitors can exist (likely as a result of the merger of two WDs) and can possibly explode as SC SNe Ia.
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