超新星2020pni的早期相：富氮星周物质的激波电离
The Early Phases of Supernova 2020pni: Shock-Ionization of the Nitrogen-Enriched Circumstellar Material
摘要：
我们提出了II型SN 2020pni的多波长观测。在爆炸后几天被归类为$\sim 1.3$，该物体显示出狭窄的（FWHM $<250\,\textrm{km}\,\textrm{s}^{-1}$）电离氦，氮和碳的复合线，就像通常在闪光光谱事件中看到的那样。使用非LTE辐射传输代码CMFGEN来模拟我们的第一个高分辨率光谱，我们推断出在$R_{\rm in}=2.5\times10^{14}\,\rm{cm}$半径处估计的原始质量损失率为$\dot{M}=(3.5-5.3)\times10^{-3}$ M $_{\odot}$ yr $^{-1}$（假设风速为$v_w=200\,\textrm{km}\,\textrm{s}^{-1}$）。此外，我们发现SN 2020 pni的祖先富含氦和氮（相对丰度分别为0.30、0.40和$8.2\times10^{-3}$）。射电上限也与密集的CSM相一致，质量损失率为$\dot M>5 \times 10^{-4}\,\rm{M_{\odot}\,yr^{-1}}$。在第一次光照后的前4天，我们还观察到氢线速度的增加（从$\sim 250\,\textrm{km}\,\textrm{s}^{-1}$到$\sim 1000\,\textrm{km}\,\textrm{s}^{-1}$），这表明了复杂的CSM。密集和受限的CSM的存在，以及其不均匀的结构，表明在爆炸前的最后一年，SN 2020pni的前身有一个质量损失增强的阶段。最后，我们比较SN 2020pni的其他冲击光电离事件的样本。我们没有发现证据的物理参数之间的相关性的爆炸和周围的这些事件的祖先CSM的特性。这支持了这样一种观点，即大质量恒星在其最后几年经历的质量损失可能是由随机现象控制的，同时，造成这种质量损失的物理机制必须是各种不同的祖先所共有的。
英文摘要：
We present multiwavelength observations of the Type II SN 2020pni. Classified at $\sim 1.3$ days after explosion, the object showed narrow (FWHM $<250\,\textrm{km}\,\textrm{s}^{-1}$) recombination lines of ionized helium, nitrogen, and carbon, as typically seen in flash-spectroscopy events. Using the non-LTE radiative transfer code CMFGEN to model our first high resolution spectrum, we infer a progenitor mass-loss rate of $\dot{M}=(3.5-5.3)\times10^{-3}$ M$_{\odot}$ yr$^{-1}$ (assuming a wind velocity of $v_w=200\,\textrm{km}\,\textrm{s}^{-1}$), estimated at a radius of $R_{\rm in}=2.5\times10^{14}\,\rm{cm}$. In addition, we find that the progenitor of SN 2020pni was enriched in helium and nitrogen (relative abundances in mass fractions of 0.30$-$0.40, and $8.2\times10^{-3}$, respectively). Radio upper limits are also consistent with a dense CSM, and a mass-loss rate of $\dot M>5 \times 10^{-4}\,\rm{M_{\odot}\,yr^{-1}}$. During the first 4 days after first light, we also observe an increase in velocity of the hydrogen lines (from $\sim 250\,\textrm{km}\,\textrm{s}^{-1}$ to $\sim 1000\,\textrm{km}\,\textrm{s}^{-1}$), which suggests a complex CSM. The presence of dense and confined CSM, as well as its inhomogeneous structure, suggest a phase of enhanced mass loss of the progenitor of SN 2020pni during the last year before explosion. Finally, we compare SN 2020pni to a sample of other shock-photoionization events. We find no evidence of correlations among the physical parameters of the explosions and the characteristics of the CSM surrounding the progenitors of these events. This favors the idea that the mass-loss experienced by massive stars during their final years could be governed by stochastic phenomena, and that, at the same time, the physical mechanisms responsible for this mass-loss must be common to a variety of different progenitors.
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