标题： 2018ivc这种不寻常的IIL/IIb型超新星的快速上升 显示英文标题

标题： The fast rise of the unusual Type IIL/IIb SN 2018ivc

摘要： 我们对邻近(10 Mpc)星系梅西耶77中的II型超新星(SN)2018ivc的测光和光谱数据集进行了分析。由于CHASE调查的高时间分辨率，我们在五小时内几乎增加了三个星等(或18 mag d$^{-1}$)，迅速观测到了SN的上升。$r$波段光变曲线呈现四个明显阶段：最大亮度在一天内达到，然后是第一次快速线性下降，接着是持续时间较短的平台期。最后是一个持续一年的缓慢线性下降。在射电重新明亮化之后，我们在爆炸四年后检测到了SN 2018ivc。早期光谱显示为蓝色、几乎无特征的连续谱，但光谱迅速演化：大约10天后，显著的H$\alpha$线开始出现，具有独特的轮廓，但光谱受到宿主星系发射线的严重污染。He I线，即$\lambda\lambda$5876,7065，也很强。在前者之上，可见到Na I双线的强吸收，表明存在不可忽略的内部红化。从其等值宽度，我们推导出宿主红化的下限为$A_V\simeq1.5$mag，而从巴尔末减幅和SN 2018ivc的$B-V$色度曲线与比较天体的匹配，得到宿主红化为$A_V\simeq3.0$mag。光谱类似于II型超新星，但具有强烈的He线。鉴于其特殊的光变曲线和光谱特征，我们认为SN 2018ivc可能是IIL型和IIb型超新星类别之间的过渡天体。此外，我们在光变曲线中发现了与星际介质相互作用的迹象，使SN 2018ivc也成为一次相互作用事件。最后，我们对SN 2018ivc的早期多波段光变曲线和光球速度进行了建模，以估计爆炸和CSM的物理参数。 显示英文摘要

摘要： We present an analysis of the photometric and spectroscopic dataset of the Type II supernova (SN) 2018ivc in the nearby (10 Mpc) galaxy Messier 77. Thanks to the high cadence of the CHASE survey, we observed the SN rising very rapidly by nearly three magnitudes in five hours (or 18 mag d$^{-1}$). The $r$-band light curve presents four distinct phases: the maximum light is reached in just one day, then a first, rapid linear decline precedes a short-duration plateau. Finally, a long, slower linear decline lasted for one year. Following a radio rebrightening, we detected SN 2018ivc four years after the explosion. The early spectra show a blue, nearly featureless continuum, but the spectra evolve rapidly: after about 10 days a prominent H$\alpha$ line starts to emerge, with a peculiar profile, but the spectra are heavily contaminated by emission lines from the host galaxy. He I lines, namely $\lambda\lambda$5876,7065, are also strong. On top of the former, a strong absorption from the Na I doublet is visible, indicative of a non-negligible internal reddening. From its equivalent width, we derive a lower limit on the host reddening of $A_V\simeq1.5$ mag, while from the Balmer decrement and a match of the $B-V$ colour curve of SN 2018ivc to that of the comparison objects, a host reddening of $A_V\simeq3.0$ mag is obtained. The spectra are similar to those of SNe II, but with strong He lines. Given the peculiar light curve and spectral features, we suggest SN 2018ivc could be a transitional object between the Type IIL and Type IIb SNe classes. In addition, we found signs of interaction with circumstellar medium in the light curve, making SN 2018ivc also an interacting event. Finally, we modelled the early multi-band light curves and photospheric velocity of SN 2018ivc to estimate the explosion and CSM physical parameters.