ASASSN-18tb: a most unusual Type Ia supernova observed by TESS and SALT
ASASSN-18tb: a most unusual Type Ia supernova observed by TESS and SALT
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DOI：
10.1093/mnras/stz1445
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发表时间：
2019-03
影响因子：
4.8
通讯作者：
P. Vallely;M. Fausnaugh;Saurabh W. Jha;M. Tucker;Y. Eweis;B. Shappee;C. Kochanek;K. Z. Stanek
中科院分区：
文献类型：
--
作者：
P. Vallely;M. Fausnaugh;Saurabh W. Jha;M. Tucker;Y. Eweis;B. Shappee;C. Kochanek;K. Z. Stanek
我们展示了对不寻常的 Ia 型超新星 ASASSN-18tb 的光度和光谱观测，包括在近六个月的时间内获得的一系列南部非洲大型望远镜光谱以及凌日系外行星勘测卫星对超新星的首次观测。我们证实了 Kollmeier 等人之前的观察。表明 ASASSN-18tb 是第一个相对正常的 Ia 型超新星，在其星云相光谱中表现出清晰的宽（~1000 km s−1）H α 发射。我们发现，这一事件最好的解释是亚钱德拉塞卡大规模爆炸，产生 $M_{\mathrm{ Ni}} \approx 0.3\,\, \rm {M}_\odot$。尽管后期有很强的 H α 特征，我们发现超新星的早期崛起没有显示出偏离单分量幂律的证据，并且最适合索引为 1.69 ± 0.04 的中等浅幂律。我们发现H α 光度在+37 d 相位初始检测后保持大致恒定，并且H α 速度演化并不追踪Fe iii λ4660 发射的速度演化。这些表明 H α 发射来自星周介质 (CSM)，而不是来自非简并伴星的扫掠材料。然而，ASASSN-18tb 在许多重要方面与其他已知的 CSM 相互作用的 Ia 型超新星有着显着的不同。这些天体的 H α 光度通常比 ASASSN-18tb 中看到的高两个数量级，使它们远离定义“正常”Ia 型超新星的经验光曲线关系。相反，ASASSN-18tb 对于低发光或过渡 SN Ia 表现出相当典型的光变曲线和光度，MR ≈ -18.1 mag。此外，ASASSN-18tb 是在早期型星系中发现的唯一一个显示出来自 CSM 相互作用的 H α 的 SN Ia。
We present photometric and spectroscopic observations of the unusual Type Ia supernova ASASSN-18tb, including a series of Southern African Large Telescope spectra obtained over the course of nearly six months and the first observations of a supernova by the Transiting Exoplanet Survey Satellite. We confirm a previous observation by Kollmeier et al. showing that ASASSN-18tb is the first relatively normal Type Ia supernova to exhibit clear broad (∼1000 km s−1) H α emission in its nebular-phase spectra. We find that this event is best explained as a sub-Chandrasekhar mass explosion producing $M_{\mathrm{ Ni}} \approx 0.3\,\, \rm {M}_\odot$. Despite the strong H α signature at late times, we find that the early rise of the supernova shows no evidence for deviations from a single-component power-law and is best fit with a moderately shallow power law of index 1.69 ± 0.04. We find that the H α luminosity remains approximately constant after its initial detection at phase +37 d, and that the H α velocity evolution does not trace that of the Fe iii λ4660 emission. These suggest that the H α emission arises from a circumstellar medium (CSM) rather than swept-up material from a non-degenerate companion. However, ASASSN-18tb is strikingly different from other known CSM-interacting Type Ia supernovae in a number of significant ways. Those objects typically show an H α luminosity two orders of magnitude higher than what is seen in ASASSN-18tb, pushing them away from the empirical light-curve relations that define ‘normal’ Type Ia supernovae. Conversely, ASASSN-18tb exhibits a fairly typical light curve and luminosity for an underluminous or transitional SN Ia, with MR ≈ −18.1 mag. Moreover, ASASSN-18tb is the only SN Ia showing H α from CSM interaction to be discovered in an early-type galaxy.