We present the photometric and spectroscopic evolution of the Type II supernova (SN II) SN 2017ivv (also known as ASASSN-17qp). Located in an extremely faint galaxy (M$_r=-10.3$ mag), SN 2017ivv shows an unprecedented evolution during the two years of observations. At early times, the light curve shows a fast rise ($\sim6-8$ days) to a peak of ${\rm M}^{\rm max}_{g}= -17.84$ mag, followed by a very rapid decline of $7.94\pm0.48$ mag per 100 days in the $V-$band. The extensive photometric coverage at late phases shows that the radioactive tail has two slopes, one steeper than that expected from the decay of $^{56}$Co (between 100 and 350 days), and another slower (after 450 days), probably produced by an additional energy source. From the bolometric light curve, we estimated that the amount of ejected $^{56}$Ni is $\sim0.059\pm0.003$ M$\odot$. The nebular spectra of SN 2017ivv show a remarkable transformation that allows the evolution to be split into three phases: (1) H$\alpha$ strong phase ($ 500$ days). We find that the nebular analysis favours a binary progenitor and an asymmetric explosion. Finally, comparing the nebular spectra of SN 2017ivv to models suggests a progenitor with a zero-age main-sequence mass of 15 -- 17 \Msun.

中文翻译：

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SN 2017ivv：过渡型II型超新星的两年演化

我们展示了 II 型超新星 (SN II) SN 2017ivv（也称为 ASASSN-17qp）的光度和光谱演化。SN 2017ivv 位于一个极其微弱的星系（M$_r=-10.3$ mag）中，在两年的观测中显示出前所未有的演变。在早期，光变曲线显示快速上升（$\sim6-8$ 天）到 ${\rm M}^{\rm max}_{g}= -17.84$ mag 的峰值，随后是非常在 $V-$ 波段中每 100 天快速下跌 $7.94\pm0.48$ mag。后期广泛的光度覆盖表明放射性尾部有两个斜率，一个比 $^{56}$Co 衰减预期的更陡（100 到 350 天之间），另一个更慢（450 天后），可能由额外的能源产生。根据热光曲线，我们估计喷射出的 $^{56}$Ni 的量为 $\sim0.059\pm0.003$M$\odot$。SN 2017ivv 的星云光谱显示出显着的转变，使得演化可以分为三个阶段：（1）H$\alpha$ 强相（$500$ 天）。我们发现星云分析有利于双星和不对称爆炸。最后，将 SN 2017ivv 的星云光谱与模型进行比较，表明前身星的零年龄主序质量为 15 - 17 \Msun。