卡内基超新星项目II：上升最慢的Ia型超新星LSQ14fmg和超超新星Ekrasekhar/03 fg事件起源的线索
Carnegie Supernova Project II: The slowest rising Type Ia supernova LSQ14fmg and clues to the origin of super-Chandrasekhar/03fg-like events
摘要：
Ia型超新星（SN Ia）LSQ 14 fmg表现出夸张的性质，这可能有助于揭示“超克拉塞卡”（或类似03 fg）群的起源。它的光谱是类03 fg超新星Ia的典型光谱，但光变曲线与任何观测到的超新星Ia都不同。LSQ 14 fmg的光变曲线上升非常缓慢。在相对于B波段最大值的-23个静止帧日，LSQ 14 fmg已经比宿主消光校正前的$M_V$ =-19等亮。观察到的颜色曲线显示从最早观察到最大值后约一周的平坦演变。近红外线曲线在J和H波段的峰值亮度超过-20.5等，远比任何类03 fg的Ia超新星的近红外观测要亮得多。在最大值过去一个月时，光学光变曲线迅速下降。早期的缓慢上升和平坦的颜色演变被解释为来自电源的额外的过量通量而不是合成的$^{56}Ni$的放射性衰变的结果。过剩通量在密度结构、质量损失率和持续时间上与渐近巨星分支（AGB）星的典型超风相互作用相匹配。在B波段最大值过去一个月左右开始的快速下降可能是活性一氧化碳（CO）形成的快速冷却的指示，这需要低温和高密度的环境。这些特点表明，AGB的祖先接近其演化的终点，核心简并的情况下，可能的爆炸机制LSQ 14 fmg。
英文摘要：
The Type Ia supernova (SN Ia) LSQ14fmg exhibits exaggerated properties which may help to reveal the origin of the "super-Chandrasekhar" (or 03fg-like) group. The optical spectrum is typical of a 03fg-like SN Ia, but the light curves are unlike those of any SNe Ia observed. The light curves of LSQ14fmg rise extremely slowly. At -23 rest-frame days relative to B-band maximum, LSQ14fmg is already brighter than $M_V$=-19 mag before host extinction correction. The observed color curves show a flat evolution from the earliest observation to approximately one week after maximum. The near-infrared light curves peak brighter than -20.5 mag in the J and H bands, far more luminous than any 03fg-like SNe Ia with near-infrared observations. At one month past maximum, the optical light curves decline rapidly. The early, slow rise and flat color evolution are interpreted to result from an additional excess flux from a power source other than the radioactive decay of the synthesized $^{56}Ni$. The excess flux matches the interaction with a typical superwind of an asymptotic giant branch (AGB) star in density structure, mass-loss rate, and duration. The rapid decline starting at around one month past B-band maximum may be an indication of rapid cooling by active carbon monoxide (CO) formation, which requires a low temperature and high density environment. These peculiarities point to an AGB progenitor near the end of its evolution and the core degenerate scenario as the likely explosion mechanism for LSQ14fmg.
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