We present multiwavelength data of SN 2020acct, a double-peaked stripped-envelope supernova (SN) in NGC 2981 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 (Mr = −18.00 ± 0.02 mag) and blue (g − r = 0.27 ± 0.03 mag) and displays spectroscopic signatures of interaction with hydrogen-free circumstellar material. The second peak is fainter (Mr = −17.29 ± 0.03 mag) and has some spectroscopic similarities to an evolved stripped-envelope SN, with strong forbidden [Ca ii] and [O ii] features. No other known double-peaked 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 SN 2020acct match models of pulsational pair instability (PPI), in which the initial peak is produced by collisions of shells of ejected material, shortly followed by core collapse. Pulsations from a star with a 72 M⊙ helium core provide an excellent match to the double-peaked light curve. The local galactic environment has a metallicity of 0.4 Z⊙, a level where massive single stars are not expected to 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 × 10−8 Mpc−3 yr−1 at z = 0.07, or <0.1% of the total core-collapse SN rate.

中文翻译：

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双 “acct”：一个独特的双峰超新星匹配脉动对不稳定性模型


我们提供了 SN 2020acct 的多波长数据，SN 2020acct 是 NGC 2981 中以 ∼150 Mpc 的双峰剥离包络超新星 （SN）。这两个峰值在时间上是不同的，最大值之间相隔 58 个静止框架日，两者之间的通量减少了 20 倍。第一个是发光的 （Mr = −18.00 ± 0.02 等） 和蓝色 （g − r = 0.27 ± 0.03 等），并显示与无氢星周材料相互作用的光谱特征。第二个峰较暗（Mr = -17.29 ± 0.03 等），与演化的剥离包络 SN 有一些光谱相似性，具有很强的禁止 [Ca ii] 和 [O ii] 特征。没有其他已知的双峰 SN 表现出与 SN 2020acct 相似的光曲线。我们发现在这段时间内，两个单独的SNe出现在同一个恒星形成区域的可能性是极不可能的，而从一个双星系统产生两个SNe需要一个难以置信的微调配置。我们发现 SN 2020acct 的特殊特性与脉动对不稳定性 （PPI） 模型相匹配，其中初始峰值是由喷射材料的壳碰撞产生的，然后是核心坍缩。来自具有 72 M⊙ 氦核的恒星的脉动与双峰光曲线完美匹配。局部银河系环境的金属丰度为 0.4 Z⊙，在这个水平上，大质量单星预计不会保留足够的质量来遇到 PPI。然而，较晚的二元合并或低金属丰度口袋可能允许所需的核心质量。我们测量 SN 2020acct 样事件的发生率为 <3.3 × 10-8 Mpc-3 yr-1，在 z = 0.07 时，或总核心坍缩 SN 率的 <0.1%。