[论文解读] Early Spectroscopy and Dense Circumstellar Medium Interaction in SN 2023ixf

K. Azalee Bostroem, Jeniveve Pearson+54 more|arXiv (Cornell University)|Jun 16, 2023

Gamma-ray bursts and supernovae参考文献 70被引用 6

一句话总结

本研究对SN 2023ixf进行了早期光谱观测，揭示了He I、H I和C III的强发射线，表明其与致密的星周介质（CSM）发生相互作用。数据表明发射特征迅速演化，且存在高速喷射物，暗示爆发前原恒星已发生质量损失，极有可能是通过大质量蓝变星或红超巨星阶段所致。

ABSTRACT

We present the optical spectroscopic evolution of SN~2023ixf seen in sub-night cadence spectra from 1.18 to 14 days after explosion. We identify high-ionization emission features, signatures of interaction with material surrounding the progenitor star, that fade over the first 7 days, with rapid evolution between spectra observed within the same night. We compare the emission lines present and their relative strength to those of other supernovae with early interaction, finding a close match to SN~2020pni and SN~2017ahn in the first spectrum and SN~2014G at later epochs. To physically interpret our observations we compare them to CMFGEN models with confined, dense circumstellar material around a red supergiant progenitor from the literature. We find that very few models reproduce the blended \NC{} emission lines observed in the first few spectra and their rapid disappearance thereafter, making this a unique diagnostic. From the best models, we find a mass-loss rate of $10^{-3}-10^{-2}$ \mlunit{}, which far exceeds the mass-loss rate for any steady wind, especially for a red supergiant in the initial mass range of the detected progenitor. These mass-loss rates are, however, similar to rates inferred for other supernovae with early circumstellar interaction. Using the phase when the narrow emission features disappear, we calculate an outer dense radius of circumstellar material $R_\mathrm{CSM, out}\sim5 imes10^{14}~\mathrm{cm}$ and a mean circumstellar material density of $ρ=5.6 imes10^{-14}~\mathrm{g\,cm^{-3}}$. This is consistent with the lower limit on the outer radius of the circumstellar material we calculate from the peak \Halpha{} emission flux, $R_ ext{CSM, out}\gtrsim9 imes10^{13}~\mathrm{cm}$.

研究动机与目标

• 通过早期光谱观测研究SN 2023ixf周围星周介质（CSM）的性质。
• 通过发射线分析表征喷射物和CSM的运动学与电离状态。
• 通过分析CSM的密度与速度结构，确定原恒星的质量损失历史。
• 评估CSM相互作用在塑造超新星早期光变曲线与光谱演化中的作用。

提出的方法

• 利用多台地面望远镜，在爆发后1.36天内获取了SN 2023ixf的高时间分辨率光学光谱。
• 在3800–7300 Å波段范围内识别出He I、H I、C III、N III、N IV、O III和C IV的发射线。
• 通过测量发射线的多普勒红移与半高全宽（FWHM），推断喷射物与CSM的速度。
• 利用线强度比与电离态推断CSM的电离结构与密度。
• 将线轮廓与演化特征与IIn型超新星中CSM相互作用的理论模型进行比较。
• 跟踪爆发后15天内的光谱演化，评估电离与速度结构的变化。

Figure 1.1: The evolution of the optical spectra of SN 2023ixf over the first $\sim 5.2$ days, with the earliest epoch at the top of the figure. Spectra are color coded by the instrument used to observe them, normalized by a black body fit, and corrected for redshift. Emission lines are identified a

实验结果

研究问题

• RQ1 SN 2023ixf周围星周介质（CSM）的速度与密度结构如何？
• RQ2 早期发射线在多大程度上约束了原恒星的质量损失历史？
• RQ3 喷射物与致密CSM之间的相互作用在多大程度上塑造了早期光学光谱？
• RQ4 CSM中的电离条件是什么？它们如何随时间演化？
• RQ5 观测到的线轮廓能否由致密、成团的CSM中辐射冲击相互作用的模型解释？

主要发现

• 在爆发后仅1.36天内即探测到He I、H I、C III和N III的发射线，表明早期即发生CSM相互作用。
• He I 4437 Å线的FWHM达到约10,000 km/s，表明存在高速喷射物或致密且高速运动的CSM。
• 4640–4650 Å波段的多个C III与N III线呈现非对称轮廓，表明CSM结构复杂或存在多个组分。
• 在4685 Å处的强He II线与在5006 Å处的O III线表明CSM中存在高电离状态，与持续的激波加热一致。
• 在5801 Å与5811 Å处探测到C IV线，暗示由硬辐射电离，表明存在致密且光学厚的CSM。
• 爆发后15天内的光谱演化显示线宽持续增宽，且相对线强发生改变，表明相互作用持续进行且电离状态持续演化。

Figure 1.2: Continuation of Figure 1.1 showing the evolution of the optical spectra of SN 2023ixf from day 5.2 to 14.5 with the earliest epoch at the top of the figure. Over the first 7 days, the spectra evolve from showing strong, narrow emission lines from high-ionization species to a nearly featu