FRAME DRAGGING, DISK WARPING, JET PRECESSING, AND DIPPED X-RAY LIGHT CURVE OF Sw J1644+57
FRAME DRAGGING, DISK WARPING, JET PRECESSING, AND DIPPED X-RAY LIGHT CURVE OF Sw J1644+57
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DOI：
10.1088/0004-637x/762/2/98
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发表时间：
2012-02
期刊：
影响因子：
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通讯作者：
W. Lei;Bing Zhang;He Gao
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文献类型：
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作者：
W. Lei;Bing Zhang;He Gao
Swift最近发现的X射线瞬态源Sw J1644+57被认为是由快速旋转的超大质量黑洞（SMBH）对星星的潮汐破坏引发的。对于这样的事件，外盘很可能与旋转的SMBH的赤道平面不重合，因为进入的星星在破裂之前很可能有一个倾斜的轨道平面。倾斜的圆盘受到Lense-Thirring扭矩的影响，由于Bardeen-Petterson效应，该扭矩趋于扭曲和翘曲。内部的圆盘倾向于与SMBH自旋对齐，而外部区域倾向于保持在恒星轨道平面内，在Bardeen-Petterson半径周围有一个过渡区。从旋转的SMBH发射的相对论性喷流将经历进动。Sw J1644+57的5-30天X射线光变曲线显示出准周期（2.7天）变化，具有明显的窄倾角。我们数值求解一个翘曲的磁盘，并提出了一个喷气进动模型调用Blandford-Znajek喷准直由附近的Bardeen-Petterson半径发射的风。通过模拟，我们表明，在X射线光变曲线的窄倾角可以再现的几何配置的范围。根据这些数据，我们推断初始恒星轨道的倾角在10°-20°范围内，喷流应该有一个适度高的洛仑兹因子，而且倾角、喷流张开角和观测者的视角使得视线扫过喷流锥的占空比略小于0.5。
The X-ray transient source Sw J1644+57 recently discovered by Swift is believed to be triggered by tidal disruption of a star by a rapidly spinning supermassive black hole (SMBH). For such events, the outer disk is very likely misaligned with respect to the equatorial plane of the spinning SMBH, since the incoming star before disruption most likely has an inclined orbital plane. The tilted disk is subject to the Lense–Thirring torque, which tends to twist and warp due to the Bardeen–Petterson effect. The inner disk tends to align with the SMBH spin, while the outer region tends to remain in the stellar orbital plane, with a transition zone around the Bardeen–Petterson radius. The relativistic jet launched from the spinning SMBH would undergo precession. The 5–30 day X-ray light curve of Sw J1644+57 shows a quasi-periodic (2.7 day) variation with noticeable narrow dips. We numerically solve a warped disk and propose a jet-precessing model by invoking a Blandford–Znajek jet collimated by a wind launched near the Bardeen–Petterson radius. Through simulations, we show that the narrow dips in the X-ray light curve can be reproduced for a range of geometric configurations. From the data we infer that the inclination angle of the initial stellar orbit is in the range of 10°–20° from the SMBH equatorial plane, that the jet should have a moderately high Lorentz factor, and that the inclination angle, jet opening angle, and observer's viewing angle are such that the duty cycle of the line of sight sweeping the jet cone is somewhat less than 0.5.