Short GRBs with Extended Emission from Magnetar Birth: Jet Formation and Collimation
Short GRBs with Extended Emission from Magnetar Birth: Jet Formation and Collimation
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DOI：
10.1111/j.1365-2966.2011.19810.x
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发表时间：
2011-06
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影响因子：
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通讯作者：
N. Bucciantini;B. Metzger;T. Thompson;E. Quataert
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作者：
N. Bucciantini;B. Metzger;T. Thompson;E. Quataert
大约1/4-1/2的短时伽马射线暴之后是持续约100 S的可变X射线发射，其注量相当于或超过了初始爆发本身。这种“扩展发射”(EE)的持续时间长、能量大，对标准的双星中子星合并模型提出了重大挑战。Mezger08最近提出，EE是由一颗强磁化中子星的自旋下降提供动力的。然而，还没有考虑到周围物质对磁星外流的影响。在这里，我们提供了相对论性原磁星风与周围10^-1 10^-3 M_\ODOT包层相互作用的含时轴对称相对论磁流体动力学模拟，该包层表示合并过程中抛出的物质、AIC之后的超新星或通过吸积盘流出的物质。相对论磁力风和膨胀的抛射物之间的碰撞在抛射物内部产生了一个磁化星云。星云中形成了一个很强的环状磁场，驱动双极喷流穿过喷出物，这类似于在长时间伽马暴情况下建立的磁星模型。我们把喷流的“爆发”时间和张开角作为风能流量点{E}和喷发质量M_Ej的函数来量化。我们证明了点{E}和θ_j是逆相关的，使得喷流的射束校正(各向同性)光度主要是M_Ej的函数。这两个可变性论点，以及能够产生明亮发射的磁星外流功率的下限，都表明磁星喷流的真实开启角必须相对较大。因此，该模型预测了在没有关联的短GRB的情况下EE是可观测的一类事件。它们可能表现为长时间的伽玛射线暴或X射线闪光，可能会被未来的全天X射线探测任务探测到。
Approximately 1/4-1/2 of short duration Gamma-Ray Bursts are followed by variable X-ray emission lasting ~ 100 s with a fluence comparable or exceeding that of the initial burst itself. The long duration and significant energy of this `extended emission'(EE) poses a major challenge to the standard binary neutron star merger model. metzger08 recently proposed that the EE is powered by the spin-down of a strongly magnetized neutron star. However, the effects of surrounding material on the magnetar outflow have not yet been considered. Here we present time-dependent axisymmetric relativistic magnetohydrodynamic simulations of the interaction of the relativistic proto-magnetar wind with a surrounding 10^-1 10^-3 M_\odot envelope, which represents material ejected during the merger; the supernova following AIC; or via outflows from the accretion disk. The collision between the relativistic magnetar wind and the expanding ejecta produces a magnetized nebula inside the ejecta. A strong toroidal magnetic field builds up in the nebula, which drives a bipolar jet out through the ejecta, similar to the magnetar model developed in the case of long duration GRBs. We quantify the `break-out' time and opening angle of the jet theta_j as a function of the wind energy flux dot{E} and ejecta mass M_ej. We show that dot{E} and theta_j are inversely correlated, such that the beaming-corrected (isotropic) luminosity of the jet is primarily a function of M_ej. Both variability arguments, and the lower limit on the power of magnetar outflows capable of producing bright emission, suggest that the true opening angle of the magnetar jet must be relatively large. The model thus predicts a class of events for which the EE is observable with no associated short GRB. These may appear as long-duration GRBs or X-Ray Flashes, which may be detected by future all-sky X-ray survey missions.