[论文解读] The Unprecedented Third Outburst of SN 2009ip: A Luminous Blue Variable Becomes a Supernova

Jon C. Mauerhan, Nathan Smith+9 more|arXiv (Cornell University)|Sep 27, 2012

Gamma-ray bursts and supernovae被引用 2

一句话总结

本文提供了证据，表明SN 2009ip在2012年的爆发是一次真正的核心坍缩型IIn型超新星，而非此前认为的终末LBV爆发，其依据是出现了展宽的巴耳末P-Cygni轮廓（蓝翼速度达-13,000 km/s），并随后演化为光度较高的IIn型超新星阶段，峰值绝对星等M_R = -18等，初始阶段较暗淡，其光度由与致密星周物质的相互作用驱动。

ABSTRACT

Some reports of supernova (SN) discoveries turn out not to be true core-collapse explosions. One such case was SN 2009ip, which was recognized to be a luminous blue variable (LBV) eruption. This source had a massive hot progenitor star identified in pre-explosion data, it had documented evidence of pre-outburst variability, and it was subsequently discovered to have a 2nd outburst in 2010. This same source rebrightened again in 2012, and early spectra showed the same narrow-line profiles as before, suggesting another LBV-like eruption. We present new photometry and spectroscopy of SN 2009ip, indicating that it has transitioned into a true SN. The most striking discovery in these data is that unlike previous reports, the spectrum exhibited Balmer lines with very broad P-Cygni profiles characteristic of normal Type II supernovae (SNe II), in addition to narrow emission lines seen in SNe IIn and LBVs. Emission components have FWHM 8000 km/s, while the P-Cygni absorption component has blue wings extending to -13,000 km/s. These velocities are typical of SNe II, but have never been associated with emission lines from a nonterminal LBV-like eruption. Initially, the peak absolute magnitude seemed fainter than that of normal SNe. However, after a brief period of fading, the source quickly brightened again to M_R=-17.5 mag over a couple days. The broad lines mostly disappeared, and the spectrum began to resemble the early optically thick phases of SNe IIn. Two weeks later the source leveled off near -18 mag, after which broad emission lines again developed in the spectrum as the source faded. We conclude that the 2012 outburst of SN 2009ip was the result of a true core-collapse SN IIn that occured when the progenitor star was in an LBV-like outburst phase, and where the SN was initially faint and then rapidly brightened due to interaction with circumstellar material (abridged).

研究动机与目标

• 确定SN 2009ip在2012年爆发的真实性质，此前该爆发被归类为大质量蓝变星（LBV）爆发。
• 解决其在2009年和2010年先前爆发后分类上的模糊性，当时这些爆发表现出LBV特征。
• 调查2012年事件是否为终末超新星爆炸，或为另一次非终末LBV爆发。
• 表征2012年爆发的光谱和光度演化，以区分超新星与LBV爆发模型。
• 评估星周物质相互作用在塑造该事件光曲线和光谱演化中的作用。

提出的方法

• 获取并分析SN 2009ip在2012年爆发期间的新光度和光谱数据。
• 将光谱特征（尤其是展宽巴耳末P-Cygni轮廓的存在与演化）与已知II型和IIn型超新星的特征进行对比。
• 通过全宽半高（FWHM）和蓝端速度测量线宽，以评估喷流动力学。
• 进行光度监测，以追踪光曲线演化，包括峰值星等和衰减行为。
• 进行光谱建模，以区分来自超新星喷流与非终末LBV爆发的辐射。
• 利用爆发前的档案数据，确认大质量炽热前身星，并将其爆发置于恒星演化史的背景下。

实验结果

研究问题

• RQ1 SN 2009ip在2012年的爆发是终末超新星爆炸，还是另一次非终末LBV爆发？
• RQ2 观测到的展宽巴耳末P-Cygni轮廓，其蓝端速度延伸至-13,000 km/s，是否表明其为核心坍缩超新星而非LBV爆发？
• RQ3 为何该源初始表现暗淡，随后在数日内迅速增亮至M_R = -17.5等，最终稳定在-18等？
• RQ4 星周物质的相互作用如何影响该事件的光谱与光度演化？
• RQ5 从展宽谱线向IIn型超新星特征的光谱演化，能否由单一物理机制解释？

主要发现

• 2012年SN 2009ip的光谱显示出展宽的巴耳末P-Cygni轮廓，其蓝翼速度延伸至-13,000 km/s，这是正常II型超新星的典型特征，而非LBV爆发的典型表现。
• 展宽谱线的发射成分具有8000 km/s的全宽半高（FWHM），与超新星喷流速度一致。
• 该源初始峰值星等较暗，但在数日内迅速增亮至M_R = -17.5等，表明因相互作用导致光度峰值延迟。
• 在达到约-18等的平台期后，展宽发射线在衰减过程中重新出现，表明与致密星周物质的持续相互作用。
• 光谱与光度演化从初始的II型超新星特征逐渐过渡为晚期的IIn型超新星特征，证实了相互作用驱动的光度增强。
• 作者得出结论：2012年的爆发是一次真正的核心坍缩型IIn型超新星，发生在前身星处于LBV样爆发阶段期间。