ASASSN-18 am/SN 2018 gk：一颗来自大质量祖先的过度发光的IIb型超新星
ASASSN-18am/SN 2018gk : An overluminous Type IIb supernova from a massive progenitor
摘要：
ASASSN-18 am/SN 2018 gk是一颗新发现的罕见的明亮富氢超新星（SNe），其峰值绝对星等为$M_V \approx -20$等，介于正常的核心坍缩SNe和超亮SNe之间。这些SNe没有显着的光谱特征的喷出物与拱星物质（CSM）的相互作用，其供电机制是有争议的。对于II型SN，ASASSN-18 am衰减非常快，光球相衰减率为$\sim6.0~\rm mag~(100 d)^{-1}$。由于HI的减弱和HeI的出现，ASASSN-18 am在光谱上是一个IIb型SN，有部分剥离的外壳。然而，它的光度和光谱演化表现出显着的差异，从典型的SNe IIb。使用辐射扩散模型，我们发现，光变曲线需要一个高的合成$\rm ^{56}Ni$质量$M_{\rm Ni} \sim0.4~M_\odot$和喷出物具有高动能$E_{\rm kin} = (7-10) \times10^{51} $ erg。引入磁星中央引擎仍然需要$M_{\rm Ni} \sim0.3~M_\odot$和$E_{\rm kin}= 3\times10^{51} $ erg。高$\rm ^{56}Ni$质量与其光谱中强的铁族星云线一致，这也类似于几个具有高$\rm ^{56}Ni$产额的SNe Ic-BL。最早的光谱显示“闪光电离”的功能，从我们估计的质量损失率$ \dot{M}\approx 2\times10^{-4}~\rm M_\odot~yr^{-1} $。这种风密度太低，无法通过喷射物-CSM相互作用为发光的光变曲线提供动力。我们测量到$H_α$的膨胀速度高达$ 17,000 $ km/s，与其他SNe II相比非常高。我们估计氧核心质量的$1.8-3.4$ $M_\odot$使用[OI]光度测量从星云相位光谱，这意味着一个祖先与零年龄的主要序列质量的$19-26$ $M_\odot$。
英文摘要：
ASASSN-18am/SN 2018gk is a newly discovered member of the rare group of luminous, hydrogen-rich supernovae (SNe) with a peak absolute magnitude of $M_V \approx -20$ mag that is in between normal core-collapse SNe and superluminous SNe. These SNe show no prominent spectroscopic signatures of ejecta interacting with circumstellar material (CSM), and their powering mechanism is debated. ASASSN-18am declines extremely rapidly for a Type II SN, with a photospheric-phase decline rate of $\sim6.0~\rm mag~(100 d)^{-1}$. Owing to the weakening of HI and the appearance of HeI in its later phases, ASASSN-18am is spectroscopically a Type IIb SN with a partially stripped envelope. However, its photometric and spectroscopic evolution show significant differences from typical SNe IIb. Using a radiative diffusion model, we find that the light curve requires a high synthesised $\rm ^{56}Ni$ mass $M_{\rm Ni} \sim0.4~M_\odot$ and ejecta with high kinetic energy $E_{\rm kin} = (7-10) \times10^{51} $ erg. Introducing a magnetar central engine still requires $M_{\rm Ni} \sim0.3~M_\odot$ and $E_{\rm kin}= 3\times10^{51} $ erg. The high $\rm ^{56}Ni$ mass is consistent with strong iron-group nebular lines in its spectra, which are also similar to several SNe Ic-BL with high $\rm ^{56}Ni$ yields. The earliest spectrum shows "flash ionisation" features, from which we estimate a mass-loss rate of $ \dot{M}\approx 2\times10^{-4}~\rm M_\odot~yr^{-1} $. This wind density is too low to power the luminous light curve by ejecta-CSM interaction. We measure expansion velocities as high as $ 17,000 $ km/s for $H_α$, which is remarkably high compared to other SNe II. We estimate an oxygen core mass of $1.8-3.4$ $M_\odot$ using the [OI] luminosity measured from a nebular-phase spectrum, implying a progenitor with a zero-age main sequence mass of $19-26$ $M_\odot$.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
