SN 2020uem: a Possible Thermonuclear Explosion within a Dense Circumstellar Medium (II). The Properties of the CSM from Polarimetry and Light-curve Modeling
SN 2020uem: a Possible Thermonuclear Explosion within a Dense Circumstellar Medium (II). The Properties of the CSM from Polarimetry and Light-curve Modeling
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DOI：
10.3847/1538-4357/acb5eb
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发表时间：
2023-01
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通讯作者：
K. Uno;T. Nagao;K. Maeda;H. Kuncarayakti;Masaomi Tanaka;K. Kawabata;T. Nakaoka;M. Kawabata;M. Yamanaka;K. Aoki;K. Isogai;M. Ogawa;A. Tajitsu;R. Imazawa
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作者：
K. Uno;T. Nagao;K. Maeda;H. Kuncarayakti;Masaomi Tanaka;K. Kawabata;T. Nakaoka;M. Kawabata;M. Yamanaka;K. Aoki;K. Isogai;M. Ogawa;A. Tajitsu;R. Imazawa
IIn/Ia-CSM 型超新星 (SNe IIn/Ia-CSM) 根据其特征光谱进行分类，其特征光谱表现出源自与星周介质 (CSM) 强相互作用的窄氢发射线以及中等质量元素的宽谱线。我们对 SN IIn/Ia-CSM 2020uem 进行了深入的后续观测，包括光度测定、光谱学和偏振测定。在本文中，我们重点关注旋光测定的结果。我们在发现后 66 天进行了成像偏振测定，并在 103 天进行了光谱偏振测定。 SN 2020uem 显示出 1.0%–1.5% 的高连续偏振，且与波长无关。此外，偏振度和位置角基本保持恒定。这些结果表明 SN 2020uem 是由与受限非球面 CSM 的强相互作用提供动力的。我们进行了简单的偏振建模，据此我们建议 SN 2020uem 具有赤道盘/环面 CSM。此外，我们还进行了半解析光曲线建模并估计了 CSM 质量。我们发现，SN 2020uem 爆炸前最后几百年的质量损失率在 0.01–0.05 M ⊙ yr−1 范围内，CSM 总质量为 0.5–4 M ⊙ 。 CSM质量不仅可以容纳红超巨星（RSG），还可以容纳红巨星（RG）或渐近巨星分支（AGB）恒星。作为 SN 2020uem 的可能祖先场景，我们提出了一个包含 RG、RSG 或 AGB 星的白矮星双星系统，特别是通过共同包层演化的合并场景，即核心简并场景或变体。
Type IIn/Ia-CSM supernovae (SNe IIn/Ia-CSM) are classified by their characteristic spectra, which exhibit narrow hydrogen emission lines originating from strong interaction with a circumstellar medium (CSM) together with broad lines of intermediate-mass elements. We performed intensive follow-up observations of SN IIn/Ia-CSM 2020uem, including photometry, spectroscopy, and polarimetry. In this paper, we focus on the results of polarimetry. We performed imaging polarimetry at 66 days and spectropolarimetry at 103 days after discovery. SN 2020uem shows a high continuum polarization of 1.0%–1.5% without wavelength dependence. Besides, the polarization degree and position angle keep roughly constant. These results suggest that SN 2020uem is powered by strong interaction with a confined and aspherical CSM. We performed simple polarization modeling, based on which we suggest that SN 2020uem has an equatorial-disk/torus CSM. Besides, we performed semi-analytic light-curve modeling and estimated the CSM mass. We revealed that the mass-loss rate in the final few hundred years immediately before the explosion of SN 2020uem is in the range of 0.01–0.05 M ⊙ yr−1, and that the total CSM mass is 0.5–4 M ⊙. The CSM mass can be accommodated by not only a red supergiant (RSG), but also by a red giant (RG) or an asymptotic giant branch (AGB) star. As a possible progenitor scenario of SN 2020uem, we propose a white dwarf binary system including an RG, RSG, or AGB star, especially a merger scenario via common envelope evolution, i.e., the core-degenerate scenario or a variant.