Fallback Accretion Model for the Years-to-decades X-Ray Counterpart to GW170817
Fallback Accretion Model for the Years-to-decades X-Ray Counterpart to GW170817
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DOI：
10.3847/2041-8213/ac1120
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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. Ioka;K. Kiuchi
中科院分区：
文献类型：
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作者：
W. Ishizaki;K. Ioka;K. Kiuchi
在中子星星合并和引力波事件GW 170817的X射线对应物中报告了一个新的成分，超过了离轴结构喷流的余辉发射。kilonova/macronova喷出物的余辉发射可以解释X射线过量，但如果光谱相同，则超过了射电观测。我们提出了一个回退吸积模型，即中子星星合并的一部分喷出物福尔斯退并在中心致密天体周围形成一个圆盘。在超爱丁顿吸积阶段，X射线光度保持在几个太阳质量的爱丁顿极限附近，射电很弱。这将遵循幂律衰减。恒定亮度阶段的持续时间传达了过去的初始回退时间尺度t0。目前的多年持续时间需要t0> 3-30秒，这表明，磁盘风，而不是动力喷出物福尔斯回落后，喷气机发射。未来几十年的观测将探索t0 10-104秒的时间尺度，大约是短伽马射线爆发的扩展发射时间。回退吸积并没有被r过程加热所阻止，这意味着裂变在年尺度上是微弱的。我们预测，由于r过程停止或后备物质耗尽，X射线对应物将在几十年内消失。
A new component was reported in the X-ray counterpart to the binary neutron star merger and gravitational-wave event GW170817, exceeding the afterglow emission from an off-axis structured jet. The afterglow emission from the kilonova/macronova ejecta may explain the X-ray excess but exceeds the radio observations if the spectrum is the same. We propose a fallback accretion model that a part of ejecta from the neutron star merger falls back and forms a disk around the central compact object. In the super-Eddington accretion phase, the X-ray luminosity stays near the Eddington limit of a few solar masses and the radio is weak, as observed. This will be followed by a power-law decay. The duration of the constant luminosity phase conveys the initial fallback timescale t 0 in the past. The current multiyear duration requires t 0 > 3–30 s, suggesting that the disk wind rather than the dynamical ejecta falls back after the jet launch. Future observations in the next decades will probe the timescale of t 0 ∼ 10–104 s, around the time of extended emission in short gamma-ray bursts. The fallback accretion has not been halted by the r-process heating, implying that fission is weak on the year scale. We predict that the X-ray counterpart will disappear in a few decades due to the r-process halting or the depletion of fallback matter.