Nuclear burning in collapsar accretion discs
Nuclear burning in collapsar accretion discs
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DOI：
10.1093/mnras/staa3002
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发表时间：
2020-08
影响因子：
4.8
通讯作者：
Y. Zenati;D. Siegel;B. Metzger;H. Perets
中科院分区：
文献类型：
--
作者：
Y. Zenati;D. Siegel;B. Metzger;H. Perets
快速旋转的大质量恒星的核心坍缩被认为是长时间伽玛射线暴（GRB）及其相关的高能量超新星（SNe）的起源。在坍缩后的早期，相对较低的角动量物质将从落入的恒星包层中循环进入位于黑洞视界外的吸积盘，从而产生高吸积速率，为GRB喷射提供动力。圆盘中部在这些小半径处的温度足够高，足以离解原子核，而从圆盘流出的中子可能丰富，可能合成r过程核。然而，在后来的时间里，对于高祖角动量，恒星包层的外层可以以更大的半径$\gtrsim 10^{7}$ cm圆，在那里核反应可以发生在盘的中间面(（例如$^{4}$ He + $^{16}$ O $\rightarrow$$^{20}$ Ne + $\gamma$）。本文通过流体动力学$\alpha$ -黏度环面模拟和19同位素核反应网络，探讨了核燃烧对坍缩吸积盘及其流出的影响，这些模拟是为了模拟坍缩演化的晚期，当环面黏度时间与包络回缩时间相当时。我们的研究结果解决了几个关键问题，例如静止燃烧和吸积与爆炸的条件以及在磁盘流出中产生$^{56}$ Ni的条件，我们认为这可能对GRB超新星的动力有重要贡献。由于位于喷射物最慢的最内层，后者可以提供必要的放射性热源，使r过程元素的光谱特征在后期GRB-SNe光谱中可见。
The core collapse of massive, rapidly-rotating stars are thought to be the progenitors of long-duration gamma-ray bursts (GRB) and their associated hyper-energetic supernovae (SNe). At early times after the collapse, relatively low angular momentum material from the infalling stellar envelope will circularize into an accretion disk located just outside the black hole horizon, resulting in high accretion rates necessary to power a GRB jet. Temperatures in the disk midplane at these small radii are sufficiently high to dissociate nuclei, while outflows from the disk can be neutron-rich and may synthesize r-process nuclei. However, at later times, and for high progenitor angular momentum, the outer layers of the stellar envelope can circularize at larger radii $\gtrsim 10^{7}$ cm, where nuclear reaction can take place in the disk midplane ((e.g.~$^{4}$He + $^{16}$O $\rightarrow$ $^{20}$Ne + $\gamma$).. Here we explore the effects of nuclear burning on collapsar accretion disks and their outflows by means of hydrodynamical $\alpha$-viscosity torus simulations coupled to a 19-isotope nuclear reaction network, which are designed to mimic the late infall epochs in collapsar evolution when the viscous time of the torus has become comparable to the envelope fall-back time. Our results address several key questions, such as the conditions for quiescent burning and accretion versus detonation and the generation of $^{56}$Ni in disk outflows, which we show could contribute significantly to powering GRB supernovae. Being located in the slowest, innermost layers of the ejecta, the latter could provide the radioactive heating source necessary to make the spectral signatures of r-process elements visible in late-time GRB-SNe spectra.