在一颗贫氢超亮超新星的晚期光谱中探测到宽H $α$发射线
Detection of Broad H$α$ Emission Lines in the Late-time Spectra of a Hydrogen-poor Superluminous Supernova
摘要：
iPTF 13 ehe是一颗贫氢超亮超新星（SLSN），z=0.3434，具有缓慢演化的光变曲线和光谱特征，与SN 2007 bi相似。它在（83-148）天（静止坐标系）内上升，达到1.3 x $10^{44}$ erg/s的最高辐射热光度，然后在0.015等非常缓慢地衰减。每日实测喷出物速度为13000 km/s。推断出的爆炸特征，如喷出物质量（67-220 $M_\odot$），总辐射和动能（分别为$10^{51}$和2 x $10^{53}$ erg），是一个缓慢发展的贫H SLSN事件的典型特征。然而，在+251天拍摄的后期光谱揭示了巴尔末α发射特征，具有宽和窄的成分，这在其他贫氢SLSNe中从未被发现过。宽分量的速度宽度约为4500 km/s，相对于窄分量有约300 km/s的蓝移。我们解释了这种广泛的H $α$发射与$\sim$ 2 $\times10^{41}$ \，erg\，s $^{-1}$的亮度之间的相互作用产生的超新星喷出物和一个离散的富氢壳，位于距离$\sim4\times10^{16}$ \，cm的爆炸现场。这种喷射-CSM相互作用导致静止帧r带LC在后期变亮。后期光谱没有被激波电离的CSM壳层完全吸收这一事实意味着它的汤姆逊散射光学深度可能<1，从而设定了CSM质量<30 $M_\odot$和体积数密度<4 x $10^8cm^{-3}$的上限。在现有的模型中，脉动对不稳定性超新星模型可以自然地解释大约40年前观测到的30 $M_\odot$ H壳层，它是从初始质量为（95-150）$M_\odot$的祖星中喷射出来的。我们估计，至少$\sim$ 15\%\的所有SLSNe-I可能有晚期巴耳末发射线。
英文摘要：
iPTF13ehe is a hydrogen-poor superluminous supernova (SLSN) at z=0.3434, with a slow-evolving light curve and spectral features similar to SN2007bi. It rises within (83-148)days (rest-frame) to reach a peak bolometric luminosity of 1.3x$10^{44}$erg/s, then decays very slowly at 0.015mag. per day. The measured ejecta velocity is 13000km/s. The inferred explosion characteristics, such as the ejecta mass (67-220$M_\odot$), the total radiative and kinetic energy ($10^{51}$ & 2x$10^{53}$erg respectively), is typical of a slow-evolving H-poor SLSN event. However, the late-time spectrum taken at +251days reveals a Balmer Halpha emission feature with broad and narrow components, which has never been detected before among other H-poor SLSNe. The broad component has a velocity width of ~4500km/s and has a ~300km/s blue-ward shift relative to the narrow component. We interpret this broad H$α$ emission with luminosity of $\sim$2$\times10^{41}$\,erg\,s$^{-1}$ as resulting from the interaction between the supernova ejecta and a discrete H-rich shell, located at a distance of $\sim4\times10^{16}$\,cm from the explosion site. This ejecta-CSM interaction causes the rest-frame r-band LC to brighten at late times. The fact that the late-time spectra are not completely absorbed by the shock ionized CSM shell implies that its Thomson scattering optical depth is likely <1, thus setting upper limits on the CSM mass <30$M_\odot$ and the volume number density <4x$10^8cm^{-3}$. Of the existing models, a Pulsational Pair Instability Supernova model can naturally explain the observed 30$M_\odot$ H-shell, ejected from a progenitor star with an initial mass of (95-150)$M_\odot$ about 40 years ago. We estimate that at least $\sim$15\%\ of all SLSNe-I may have late-time Balmer emission lines.
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