SN 2007 if的近超新星工厂观测：首次测量超超新星的总质量
Nearby Supernova Factory Observations of SN 2007if: First Total Mass Measurement of a Super-Chandrasekhar-Mass Progenitor
摘要：
本文报道了SN 2007 if的光度和光谱观测结果，SN 2007 if是一颗位于非常微弱（M_g = -14.10）的主星系中的过亮（M_V = -20.4）、红色（B带最大值B-V = 0.16）、缓慢上升（t_rise = 24天）的Ia型超新星。在B波段最大光过去5天的光谱与超拉塞卡质量的候选者SN Ia 2003 fg直接匹配，显示Si II和C II的速度约为9000 km/s。高信噪比的SN光谱时间序列的共同添加揭示没有钠I D吸收，这表明在宿主星系可以忽略不计的变红，和后期的颜色演化具有相同的斜率正常SNe Ia的里拉关系。喷出物似乎是很好的混合，没有强的最大值在I-带和铁峰线出现在近最大光光谱的多样性。SN 2007如果也显示了一个平台的Si II速度延长到+10天，我们解释为证据的致密壳在SN喷出物。我们计算的SN的热光变曲线，并使用它和\ion{Si}{2}的速度演化来约束壳层和下面的SN喷出物的质量，并证明，SN 2007如果是强烈不一致的一个拉塞卡质量的情况。在适用于双简并合并的“夯实爆炸”模型的背景下，并假设没有宿主灭绝，我们估计系统的总质量为2.4 +/- 0.2太阳质量，其中1.6 +/- 0.1太阳质量的镍-56和0.3-0.5太阳质量的未燃烧碳/氧包层。我们的模拟表明，壳卷吸的运动学提供了一个更有效的机制，比不完全的核燃烧产生的典型的超亚克拉塞卡质量SNeIa的低速度。
英文摘要：
We present photometric and spectroscopic observations of SN 2007if, an overluminous (M_V = -20.4), red (B-V = 0.16 at B-band maximum), slow-rising (t_rise = 24 days) type Ia supernova in a very faint (M_g = -14.10) host galaxy. A spectrum at 5 days past B-band maximum light is a direct match to the super-Chandrasekhar-mass candidate SN Ia 2003fg, showing Si II and C II at ~9000 km/s. A high signal-to-noise co-addition of the SN spectral time series reveals no Na I D absorption, suggesting negligible reddening in the host galaxy, and the late-time color evolution has the same slope as the Lira relation for normal SNe Ia. The ejecta appear to be well mixed, with no strong maximum in I-band and a diversity of iron-peak lines appearing in near-maximum-light spectra. SN2007 if also displays a plateau in the Si II velocity extending as late as +10 days, which we interpret as evidence for an overdense shell in the SN ejecta. We calculate the bolometric light curve of the SN and use it and the \ion{Si}{2} velocity evolution to constrain the mass of the shell and the underlying SN ejecta, and demonstrate that SN2007 if is strongly inconsistent with a Chandrasekhar-mass scenario. Within the context of a "tamped detonation" model appropriate for double-degenerate mergers, and assuming no host extinction, we estimate the total mass of the system to be 2.4 +/- 0.2 solar masses, with 1.6 +/- 0.1 solar masses of nickel-56 and with 0.3-0.5 solar masses in the form of an envelope of unburned carbon/oxygen. Our modeling demonstrates that the kinematics of shell entrainment provide a more efficient mechanism than incomplete nuclear burning for producing the low velocities typical of super-Chandrasekhar-mass SNeIa.
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