We present DES16C3cje, a low-luminosity, long-lived type II supernova (SN II) at redshift 0.0618, detected by the Dark Energy Survey (DES). DES16C3cje is a unique SN. The spectra are characterized by extremely narrow photospheric lines corresponding to very low expansion velocities of ≲ 1500 km s−1, and the light curve shows an initial peak that fades after 50 days before slowly rebrightening over a further 100 days to reach an absolute brightness of Mr ∼ −15.5 mag. The decline rate of the late-time light curve is then slower than that expected from the powering by radioactive decay of 56Co, but is comparable to that expected from accretion power. Comparing the bolometric light curve with hydrodynamical models, we find that DES16C3cje can be explained by either i) a low explosion energy (0.11 foe) and relatively large 56Ni production of 0.075 M⊙ from a ∼15 M⊙ red supergiant progenitor typical of other SNe II, or ii) a relatively compact ∼40 M⊙ star, explosion energy of 1 foe, and 0.08 M⊙ of 56Ni. Both scenarios require additional energy input to explain the late-time light curve, which is consistent with fallback accretion at a rate of ∼0.5 × 10−8 M⊙ s−1.

中文翻译：

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DES16C3cje：一颗低亮度、寿命长的超新星

我们展示了 DES16C3cje，这是一颗由暗能量巡天 (DES) 探测到的红移 0.0618 处的低光度、长寿命的 II 型超新星 (SN II)。DES16C3cje 是唯一的 SN。光谱的特点是极窄的光球线对应于 ≲ 1500 km s-1 的极低膨胀速度，光变曲线显示初始峰值在 50 天后逐渐消失，然后在 100 天后缓慢重新变亮，达到绝对亮度Mr ∼ -15.5 mag。后期光变曲线的下降速度比 56Co 放射性衰变动力所预期的要慢，但与吸积动力所预期的速度相当。将辐射热光曲线与流体动力学模型进行比较，我们发现 DES16C3cje 可以通过 i) 低爆炸能 (0.11 foe) 和相对较大的 56Ni 产量来解释 0。075 M⊙ 来自 ∼15 M⊙ 红超巨星前身，是其他 SNe II 的典型特征，或者 ii) 一颗相对致密的 ∼40 M⊙ 恒星，爆炸能量为 1 个敌人，0.08 M⊙ 为 56Ni。两种情况都需要额外的能量输入来解释后期光变曲线，这与回退吸积速度为∼0.5 × 10−8 M⊙ s−1 一致。