The Nebular Spectra of the Hypernova SN 1998bw and Evidence for Asymmetry
The Nebular Spectra of the Hypernova SN 1998bw and Evidence for Asymmetry
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DOI：
10.1086/322420
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发表时间：
2001-06
期刊：
影响因子：
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通讯作者：
P. Mazzali;K. Nomoto;F. Patat;K. Maeda
中科院分区：
文献类型：
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作者：
P. Mazzali;K. Nomoto;F. Patat;K. Maeda
本文研究了高能Ic型超新星SN 1998bw（超新星）的星云光谱。星云相的过渡发生在爆发后约100天的时期，这被认为是符合GRB 980425。在星云时代的早期，光谱显示出典型超新星（SN）Ic光谱的特征，具有强的[O I]，Ca II和Mg I]线和[Fe II]线。然而，[Fe II]线对于SN Ic是异常强的。此外，不同元素的线具有不同的宽度，指示不同的膨胀速度。特别是，铁似乎比氧膨胀得更快。此外，[O I]星云谱线比[Fe II]谱线下降得更慢，表明γ射线沉积在缓慢移动的O主导区域。这些事实表明爆炸是非球面的。[Fe III]星云线的缺乏可以理解，如果喷出物显着聚集。一个示意图是什么这个非常不寻常的恒星爆炸可能看起来像是提出。
The nebular spectra of the energetic Type Ic supernova SN 1998bw (hypernova) are studied. The transition to the nebular phase occurred at an epoch of about 100 days after outburst, which is assumed to coincide with GRB 980425. Early in the nebular epoch the spectra show the characteristics of a typical supernova (SN) Ic spectrum, with strong lines of [O I], Ca II, and Mg I], and lines of [Fe II]. However, the [Fe II] lines are unusually strong for an SN Ic. Also, lines of different elements have different widths, indicating different expansion velocities. In particular, iron appears to expand more rapidly than oxygen. Furthermore, the [O I] nebular lines decline more slowly than the [Fe II] ones, signaling deposition of γ-rays in a slowly moving O-dominated region. These facts suggest that the explosion was aspherical. The absence of [Fe III] nebular lines can be understood if the ejecta are significantly clumped. A schematic picture of what this very unusual stellar explosion may have looked like is presented.