寻找IIb型超新星中的前兆爆发
Search for precursor eruptions among Type IIb supernovae
摘要：
几颗IIb型超新星（SNe）的祖星显示出扩展氢包层的迹象。这些包层可能是明亮的高能爆炸前事件的结果，即所谓的前兆爆发。我们使用的Palomar瞬态工厂（PTF）爆炸前的27个附近的IIb型SNe的样本观察，寻找这样的前体在最后几年的SN爆炸之前。结合15天仓的观测结果，没有发现任何前兆，我们计算了前兆率的绝对震级依赖上限。在90%的置信水平下，IIb型超新星在爆炸前的最后3.5年内和最后一年的$<0.56$事件中，平均$<0.86$前兆与绝对$R$ -带星等$-14$一样亮。相比之下，SNe IIn中的前体具有高$\gtrsim 5$倍的速率。解开一个低质量恒星包层所需的动能与几周前体的辐射能量相当，而在我们的样本中，最近的SNe可以探测到。因此，质量喷射，如果他们是常见的，在这样的SNe，是辐射效率低，或有持续时间超过几个月。实际上，当使用60天的箱时，在SN 2012 cs之前检测到微弱的前体候选物（$\sim2$ %假警报概率）。我们还报告了SN 2011 dh的前身的检测，在爆炸前的最后两年中没有显示出可检测的变化。SN 2012 P的前身仍然存在，因此可能是一个紧凑的星团，或者是一个不相关的物体。
英文摘要：
The progenitor stars of several Type IIb supernovae (SNe) show indications for extended hydrogen envelopes. These envelopes might be the outcome of luminous energetic pre-explosion events, so-called precursor eruptions. We use the Palomar Transient Factory (PTF) pre-explosion observations of a sample of 27 nearby Type IIb SNe to look for such precursors during the final years prior to the SN explosion. No precursors are found when combining the observations in 15-day bins, and we calculate the absolute-magnitude-dependent upper limit on the precursor rate. At the 90% confidence level, Type IIb SNe have on average $<0.86$ precursors as bright as absolute $R$-band magnitude $-14$ in the final 3.5 years before the explosion and $<0.56$ events over the final year. In contrast, precursors among SNe IIn have a $\gtrsim 5$ times higher rate. The kinetic energy required to unbind a low-mass stellar envelope is comparable to the radiated energy of a few-weeks-long precursor which would be detectable for the closest SNe in our sample. Therefore, mass ejections, if they are common in such SNe, are radiatively inefficient or have durations longer than months. Indeed, when using 60-day bins a faint precursor candidate is detected prior to SN 2012cs ($\sim2$% false-alarm probability). We also report the detection of the progenitor of SN 2011dh which does not show detectable variability over the final two years before the explosion. The suggested progenitor of SN 2012P is still present, and hence is likely a compact star cluster, or an unrelated object.
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