A common central engine for long gamma-ray bursts and Type Ib/c supernovae
A common central engine for long gamma-ray bursts and Type Ib/c supernovae
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DOI：
10.1093/mnras/stx2083
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发表时间：
2017-04
影响因子：
4.8
通讯作者：
E. Sobacchi;J. Granot;O. Bromberg;M. Sormani
中科院分区：
文献类型：
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作者：
E. Sobacchi;J. Granot;O. Bromberg;M. Sormani
持续时间长、光谱软的伽马射线暴 (GRB) 与 Ic 型核心塌陷 (CC) 超新星 (SNe) 相关，因此是由大质量恒星的死亡产生的。在塌缩星模型中，由中央发动机发射的喷射流必须钻出祖星才能产生伽马射线暴。大多数这些喷流不会爆发，而是被“窒息”在恒星内部，因为中央引擎的活动时间 $t_{\rm e}$ 不够长。对长软GRB持续时间分布进行建模，假设其中央发动机活动时间呈幂律分布，$\propto t_{\rm e}^{-\alpha}$ for $t_{\rm e}>t_{\rm b}$，我们发现一个陡峭的分布（$\alpha\sim4$）和典型的GRB喷流爆发时间 $t_{\rm b}\sim 60\text{ s}$ 在恒星框架中。后者表明祖星周围存在低密度、扩展的包层，类似于之前推断的低光度伽玛暴。将该幂律的有效性范围推断为低于直接可观察到的 $t_{\rm e}<t_{\rm b}$，仅通过 $\sim$4-5 的因子即可产生足够的事件来解释所有 Ib/c 型 SNe。这种外推是必要的，以避免微调中央引擎活动时间与突破时间的分布，这可能是不相关的。我们推测发射相对论性射流的中央发动机可能在所有 Ib/c 型超新星中运行。在这种情况下，通用中央发动机的存在意味着 (i) 喷气机可能对 SN 的能量有显着贡献； （ii）各种观测特征，例如爆炸的非球面性，可能与喷流与恒星的相互作用直接相关。
Long-duration, spectrally-soft Gamma-Ray Bursts (GRBs) are associated with Type Ic Core Collapse (CC) Supernovae (SNe), and thus arise from the death of massive stars. In the collapsar model, the jet launched by the central engine must bore its way out of the progenitor star before it can produce a GRB. Most of these jets do not break out, and are instead "choked" inside the star, as the central-engine activity time, $t_{\rm e}$, is not long enough. Modelling the long-soft GRB duration distribution assuming a power-law distribution for their central-engine activity times, $\propto t_{\rm e}^{-\alpha}$ for $t_{\rm e}>t_{\rm b}$, we find a steep distribution ($\alpha\sim4$) and a typical GRB jet breakout time of $t_{\rm b}\sim 60\text{ s}$ in the star's frame. The latter suggests the presence of a low-density, extended envelope surrounding the progenitor star, similar to that previously inferred for low-luminosity GRBs. Extrapolating the range of validity of this power law below what is directly observable, to $t_{\rm e}<t_{\rm b}$, by only a factor of $\sim$4-5 produces enough events to account for all Type Ib/c SNe. Such extrapolation is necessary to avoid fine-tuning the distribution of central engine activity times with the breakout time, which are presumably unrelated. We speculate that central engines launching relativistic jets may operate in all Type Ib/c SNe. In this case, the existence of a common central engine would imply that (i) the jet may significantly contribute to the energy of the SN; (ii) various observational signatures, like the asphericity of the explosion, could be directly related to jet's interaction with the star.