短伽马射线暴：吸积盘的质量和外流的初始半径
Short Gamma-ray Bursts: the mass of the accretion disk and the initial radius of the outflow
摘要：
在这项工作中，我们估计吸积盘的质量在特定的情况下的双星中子星合并与目前的观测数据。假设短伽马射线暴（GRB）的外流是由中微子-反中微子湮灭驱动的，我们估计样品中大约一半的短暴的盘质量为$\sim 0.01-0.1 M_\odot$，与数值模拟中得到的结果一致。在其他一些短伽玛暴中发现的大质量盘（$\sim {\rm several} 0.1 M_\odot$）可能指向更有效的能量提取磁性过程或中子星和黑洞双星的祖先。我们的结果表明，一些短爆发可能是由于双中子星的合并，是有希望的引力波辐射源。对于未来的短伽玛暴与同步引力波探测，磁盘质量可能会被可靠地推断和我们的方法的有效性将被测试。我们还提出了一种方法来约束重子流出的初始半径，它是发射（$R_0$），而不需要确定一个理想的热谱。然后，我们将其应用于GRB 090510，得到了$R_0 \lesssim 6.5\times 10^{6}(Γ_{\rm ph}/2000)^{-4}$ cm，这表明中心引擎是一个质量为$< 22 M_\odot(Γ_{\rm ph}/2000)^{-4}$的黑洞，其中$Γ_{\rm ph}$是光球半径处流出的大部分洛伦兹因子。
英文摘要：
In this work we estimate the accretion-disk mass in the specific scenario of binary-neutron-star-merger with current observational data. Assuming that the outflows of short Gamma-ray Bursts (GRBs) are driven via neutrino-antineutrino annihilation we estimate the disk mass of about half of short bursts in the sample to be $\sim 0.01-0.1 M_\odot$, in agreement with that obtained in the numerical simulations. Massive disks ($\sim {\rm several} 0.1 M_\odot$) found in some other short GRBs may point to the more efficient magnetic process of energy extraction or the neutron star and black hole binary progenitor. Our results suggest that some short bursts may be really due to the coalescence of double neutron stars and are promising gravitational wave radiation sources. For future short GRBs with simultaneous gravitational-wave detections, the disk mass may be reliably inferred and the validity of our approach will be tested. We also propose a method to constrain the initial radius of a baryonic outflow where it is launched ($R_0$) without the need of identifying an ideal thermal spectrum. We then apply it to GRB 090510 and get that $R_0 \lesssim 6.5\times 10^{6}(Γ_{\rm ph}/2000)^{-4}$ cm, suggesting that the central engine is a black hole with a mass $< 22 M_\odot(Γ_{\rm ph}/2000)^{-4}$, where $Γ_{\rm ph}$ is the bulk Lorentz factor of the outflow at the photospheric radius.
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