Fallback Accretion Halted by R-process Heating in Neutron Star Mergers and Gamma-Ray Bursts
Fallback Accretion Halted by R-process Heating in Neutron Star Mergers and Gamma-Ray Bursts
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DOI：
10.3847/1538-4357/ac23d9
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发表时间：
2021-04
期刊：
影响因子：
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通讯作者：
W. Ishizaki;K. Kiuchi;K. Ioka;S. Wanajo
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作者：
W. Ishizaki;K. Kiuchi;K. Ioka;S. Wanajo
具有macronova/kilonova的引力波事件GW 170817表明，两颗中子星的合并产生了具有放射性的物质，包括r-过程核合成。一部分喷出物不可避免地福尔斯落回中心物体，可能为短伽马射线暴（sGRB）的长期活动提供动力，例如延长和平台发射。我们调查回退吸积与r-过程加热进行一维流体动力学模拟和开发一个半解析模型。我们发现，通常的回落率dM/dt <$t-5/3被加热停止，因为压力梯度加速喷出物超过逃逸速度。抑制是陡峭的比Chevalier的幂律模型，通过邦迪吸积在一个转身半径。GW 170817型γ-过程加热的特征停止时间尺度为104-108 s，这比sGRB持久发射的典型时间尺度更长。停止时间尺度对r过程的不确定性很敏感。未来对回落停止的观测可能会在一年的尺度上限制r过程加热。
The gravitational wave event GW170817 with a macronova/kilonova shows that a merger of two neutron stars ejects matter with radioactivity including r-process nucleosynthesis. A part of the ejecta inevitably falls back to the central object, possibly powering long-lasting activities of a short gamma-ray burst (sGRB), such as extended and plateau emissions. We investigate fallback accretion with r-process heating by performing one-dimensional hydrodynamic simulations and developing a semi-analytical model. We show that the usual fallback rate dM/dt ∝ t −5/3 is halted by the heating because pressure gradients accelerate ejecta beyond an escape velocity. The suppression is steeper than Chevalier’s power-law model through Bondi accretion within a turn-around radius. The characteristic halting timescale is ∼104–108 s for the GW170817-like r-process heating, which is longer than the typical timescale of the long-lasting emission of sGRBs. The halting timescale is sensitive to the uncertainty of the r-process. Future observations of fallback halting could constrain the r-process heating on the scale of a year.