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arXiv 1605.02491astro-ph.HEastro-ph.SR
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iPTF15dtg:一个双峰型Ic超新星,来自一个巨大的祖先

iPTF15dtg: a double-peaked Type Ic Supernova from a massive progenitor

F. Taddia, C. Fremling, J. Sollerman, A. Corsi, A. Gal-Yam, E. Karamehmetoglu, R. Lunnan, B. Bue, M. Ergon, M. Kasliwal, P. M. Vreeswijk, P. R. Wozniak

摘要:

Ic型超新星(SNe Ic)产生于贫氢(和氦)恒星的核心坍缩,这些恒星可能是单个WR恒星,也可能是被伴星剥离了外壳的低质量恒星。它们的光变曲线是放射性供电的,并且通常显示出快速上升到峰值($\sim$ 10-15 d),而没有任何早期(最初几天)发射凸起(除了宽线SNe Ic),这有时见于其他类型的条带包络SNe(例如,IIb型SN 1993 J和Ib型SN 2008 D)。我们已经研究了iPTF 15 dtg,光谱正常的SN Ic与早期过剩的光学光变曲线,随后由一个长($\sim$ 30天)上升到主峰。这是第一个观测到的光谱正常双峰SN Ic。我们的目标是确定这次爆炸及其前身恒星的性质。iPTF 15 dtg的光学光度和光谱是用多个望远镜获得的。由此产生的光变曲线和光谱序列进行了分析和建模与流体动力学和分析模型,特别侧重于早期的排放。结果iPTF 15 dtg是一个缓慢上升的SN Ic,类似于SN 2011 bm。流体动力学模型的测热特性揭示了一个大的喷出物质量($\sim$ 10 $M_{\odot}$)和强大的$^{56}$镍混合。如果我们考虑到祖星周围存在一个扩展的($\sim$ 500 R $_{\odot}$)、低质量($\sim$ 0.045 M $_{\odot}$)包层,那么早期的发光就可以重现。早期峰值的替代方案,如与伴星的相互作用,来自祖星表面的冲击爆发(SBO)冷却尾部,或磁星驱动的SBO都不受欢迎。巨大的喷出物质量和恒星周围存在的H和He自由扩展物质表明,iPTF 15 dtg的前身是一颗大质量($\gtrsim$ 35 M $_{\odot}$)WR恒星,遭受了强烈的质量损失。

英文摘要:

Type Ic supernovae (SNe Ic) arise from the core-collapse of H (and He) poor stars, which could be either single WR stars or lower-mass stars stripped of their envelope by a companion. Their light curves are radioactively powered and usually show a fast rise to peak ($\sim$10-15 d), without any early (first few days) emission bumps (with the exception of broad-lined SNe Ic) as sometimes seen for other types of stripped-envelope SNe (e.g., Type IIb SN 1993J and Type Ib SN 2008D). We have studied iPTF15dtg, a spectroscopically normal SN Ic with an early excess in the optical light curves followed by a long ($\sim$30 d) rise to the main peak. It is the first spectroscopically-normal double-peaked SN Ic observed. We aim to determine the properties of this explosion and of its progenitor star. Optical photometry and spectroscopy of iPTF15dtg was obtained with multiple telescopes. The resulting light curves and spectral sequence are analyzed and modelled with hydrodynamical and analytical models, with particular focus on the early emission. Results. iPTF15dtg is a slow rising SN Ic, similar to SN 2011bm. Hydrodynamical modelling of the bolometric properties reveals a large ejecta mass ($\sim$10 $M_{\odot}$) and strong $^{56}$Ni mixing. The luminous early emission can be reproduced if we account for the presence of an extended ($\sim$500 R$_{\odot}$), low-mass ($\sim$0.045 M$_{\odot}$) envelope around the progenitor star. Alternative scenarios for the early peak, such as the interaction with a companion, a shock-breakout (SBO) cooling tail from the progenitor surface, or a magnetar-driven SBO are not favored. The large ejecta mass and the presence of H and He free extended material around the star suggest that the progenitor of iPTF15dtg was a massive ($\gtrsim$ 35 M$_{\odot}$) WR star suffering strong mass loss.

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