双“acct”：一颗与脉动对不稳定性模型相符的独特双峰超新星
Double "acct": a distinct double-peaked supernova matching pulsational pair-instability models
AI总结：
本文通过多波段观测揭示SN2020acct是一颗独特的双峰剥离包层超新星，其光变曲线与72倍太阳质量氦核恒星的脉动对不稳定性模型高度吻合，并测得此类事件发生率低于核心坍缩超新星总率的0.1%。
摘要：
我们展示了SN2020acct的多波段数据，这是一颗位于约150 Mpc处NGC2981中的双峰剥离包层超新星（SN）。两个峰在时间上明显分离，峰值间隔为58个静止系天，其间流量下降了20倍。第一个峰明亮（M$_{r}$ = -18.00 $\pm$ 0.02 mag），颜色偏蓝（g - r = 0.27 $\pm$ 0.03 mag），并显示出与无氢星周物质相互作用的谱学特征。第二个峰较暗（M$_{r}$ = -17.29 $\pm$ 0.03 mag），谱学上与演化后的剥离包层超新星相似，具有强的混合禁线[Ca II]和[O II]特征。已知的其他双峰超新星均未表现出与SN 2020acct相似的光变曲线。我们发现两颗独立超新星在该时间范围内出现在同一恒星形成区的可能性极低，而要从单个双星系统中产生两颗超新星则需要一种难以置信的精细调节构型。我们发现SN2020acct的特殊性质与脉动对不稳定性（PPI）模型相符，在该模型中，初始峰由抛射物质壳层的碰撞产生，紧随其后发生终结性爆炸。来自一个具有72 M$_{\odot}$氦核的恒星的脉动与双峰光变曲线高度吻合。所在星系环境具有0.4 Z$_{\odot}$的金属丰度，在这一水平上，大质量单星预计无法保留足够质量以经历PPI。然而，晚期双星并合或低金属丰度区域可能提供所需的核质量。我们测得类似SN 2020acct的事件发生率在z = 0.07处为$<3.3\times10^{-8}$ Mpc$^{-3}$ yr$^{-1}$，即低于核心坍缩超新星总发生率的0.1%。
英文摘要：
We present multi-wavelength data of SN2020acct, a double-peaked stripped-envelope supernova (SN) in NGC2981 at ~150 Mpc. The two peaks are temporally distinct, with maxima separated by 58 rest-frame days, and a factor of 20 reduction in flux between. The first is luminous (M$_{r}$ = -18.00 $\pm$ 0.02 mag), blue (g - r = 0.27 $\pm$ 0.03 mag), and displays spectroscopic signatures of interaction with hydrogen-free circumstellar material. The second peak is fainter (M$_{r}$ = -17.29 $\pm$ 0.03 mag), and spectroscopically similar to an evolved stripped-envelope SNe, with strong blended forbidden [Ca II] and [O II] features. No other known double-peak SN exhibits a light curve similar to that of SN 2020acct. We find the likelihood of two individual SNe occurring in the same star-forming region within that time to be highly improbable, while an implausibly fine-tuned configuration would be required to produce two SNe from a single binary system. We find that the peculiar properties of SN2020acct match models of pulsational pair instability (PPI), in which the initial peak is produced by collisions of shells of ejected material, shortly followed by a terminal explosion. Pulsations from a star with a 72 M$_{\odot}$ helium core provide an excellent match to the double-peaked light curve. The local galactic environment has a metallicity of 0.4 Z$_{\odot}$, a level where massive single stars are not expected retain enough mass to encounter the PPI. However, late binary mergers or a low-metallicity pocket may allow the required core mass. We measure the rate of SN 2020acct-like events to be $<3.3\times10^{-8}$ Mpc$^{-3}$ yr$^{-1}$ at z = 0.07, or <0.1% of the total core-collapse SN rate.
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