[论文解读] Multi-epoch high-resolution spectroscopy of SN2011fe - Linking the progenitor to its environment

F. Patat, Martin Cordiner+11 more|arXiv (Cornell University)|Dec 1, 2011

Gamma-ray bursts and supernovae参考文献 47被引用 41

一句话总结

本研究利用SN 2011fe的多 epoch 高分辨率光谱，探测其周围介质环境，并将前身体特性与周围物质联系起来。研究发现吸收特征的变异性极小且消光程度低，表明环境极为洁净，与非巨星、可能为双简并前身体系统的特征一致，且存在尺度≤100 AU的ISM结构。

ABSTRACT

This study attempts to establish a link between the reasonably well known nature of the progenitor of SN2011fe and its surrounding environment. This is done with the aim of enabling the identification of similar systems in the vast majority of the cases, when distance and epoch of discovery do not allow a direct approach. To study the circumstellar environment of SN2011fe we have obtained high-resolution spectroscopy of SN2011fe on 12 epochs, from 8 to 86 days after the estimated date of explosion, targeting in particular at the time evolution of CaII and NaI. Three main absorption systems are identified from CaII and NaI, one associated to the Milky Way, one probably arising within a high-velocity cloud, and one most likely associated to the halo of M101. The Galactic and host galaxy reddening, deduced from the integrated equivalent widths (EW) of the NaI lines are E(B-V)=0.011+/-0.002 and E(B-V)=0.014+/-0.002 mag, respectively. The host galaxy absorption is dominated by a component detected at the same velocity measured from the 21-cm HI line at the projected SN position (~180 km/s). During the ~3 months covered by our observations, its EW changed by 15.6+/-6.5 mA. This small variation is shown to be compatible with the geometric effects produced by therapid SN photosphere expansion coupled to the patchy fractal structure of the ISM. The observed behavior is fully consistent with ISM properties similar to those derived for our own Galaxy, with evidences for structures on scales <100 AU. SN2011fe appears to be surrounded by a "clean" environment. The lack of blue-shifted, time-variant absorption features is fully consistent with the progenitor being a binary system with a main-sequence, or even another degenerate star.

研究动机与目标

• 利用高分辨率光谱，将SN 2011fe的前身体系统与周围星际介质（ISM）环境联系起来。
• 确定星周物质（CSM）特征（如时间相关的吸收）是否能约束前身体的性质。
• 通过分析ISM的痕迹，评估不同前身体通道（如单简并与双简并）对Ia型超新星速率的贡献。
• 评估ISM吸收作为前身体特性代理的可靠性，同时考虑视线方向和几何效应的影响。
• 为在遥远超新星中识别类似系统提供基准，因为在这些情况下直接研究前身体不可行。

提出的方法

• 使用多个望远镜（Mercator、TNG、NOT 和 Copernico）在爆炸后8至86天内，对SN 2011fe进行了12个 epoch 的高分辨率光谱观测。
• 聚焦于Ca ii 和 Na i 吸收线的时间演化，以探测可变的星周或星际物质。
• 通过吸收线等效宽度（EW）测量，利用EW与消光之间的关系，推导出总消光及组分特定的EB−V值。
• 将观测到的吸收变异性与SN光球膨胀在分形、不连续ISM结构中的理论模型进行比较。
• 使用日心速度修正及来自21-cm H I线数据的径向速度测量，识别宿主星系和银河系组分。
• 评估SN光球膨胀引起的几何效应，对观测吸收深度和宽度的影响，以推断ISM结构的尺度长度。

实验结果

研究问题

• RQ1 SN 2011fe的星周环境是否表现出时间可变的吸收特征，表明前身体存在质量损失？
• RQ2 银河系、高速云以及宿主星系M101对观测到的Na i和Ca ii吸收组分的贡献各是多少？
• RQ3 观测到的吸收变异性与SN光球在不连续ISM中的膨胀预测相比如何？
• RQ4 缺乏蓝移、时间可变的吸收特征是否可用于排除前身体系统中存在非简并巨星伴星的可能性？
• RQ5 观测到的ISM环境在多大程度上支持SN 2011fe为双简并前身体的假设？

主要发现

• 识别出三个主要吸收组分：一个来自银河系（EB−V = 0.011 ± 0.002 mag），一个来自高速云，一个来自宿主星系M101（EB−V = 0.014 ± 0.002 mag）。
• 宿主星系吸收组分的中心速度约为~180 km s⁻¹，与SN投影位置处21-cm H I线的径向速度一致。
• 宿主星系Na i线的等效宽度在约3个月内变化了15.6 ± 6.5 mÅ，与分形ISM中SN光球膨胀引起的几何效应一致。
• 观测到的变异性与银河系性质相似的ISM特性完全兼容，其结构尺度≤100 AU。
• 未检测到显著的蓝移、时间可变的吸收特征，表明缺乏致密且质量巨大的星周物质。
• 环境特征与前身体系统在爆炸前未发生显著质量损失一致，支持主序星或简并伴星的双简并前身体情景。