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arXiv 1111.2802astro-ph.HEgr-qc
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黑洞对恒星潮汐扰动的喷流

Jets from Tidal Disruptions of Stars by Black Holes

Julian H. Krolik, Tsvi Piran

摘要:

一般认为,黑洞对主序星的潮汐干扰会导致紫外辐射占主导地位的信号。然而,如果黑洞快速旋转,并且黑洞视界上的极向磁场强度与内部吸积盘压力相当,则可能形成一个强大的喷流,其亮度可以很容易地超过热紫外亮度。当喷流光束指向地球时,其非热光度可以主导发射光谱。热分量和非热分量随时间不同地衰减。特别是,热发射应保持大致恒定的一个显着的时间后,最大吸积期,开始减少后,只有一个延迟,而在峰值吸积率,非热喷流发射衰减,但然后达到一个平台。这两个转变都与一个特征时间尺度$t_{\rm Edd}$有关,在这个时间尺度上,吸积速率低于爱丁顿。利用这个时间尺度在一个新的参数推断形式主义的潮汐中断事件与显着的排放从喷流,我们分析了最近的耀斑源斯威夫特J2058。这与主序星太阳型恒星被质量为$\sim 4 \times 10^7 M_{\odot}$的黑洞破坏的事件是一致的。从这个源的非热发射的平坦阶段的开始可能可以在后期的光变曲线中看到。在这个耀斑的第一个$\simeq 40$ d上的光学测光也与这张图片一致,但只是弱约束,因为测热校正是非常不确定的。我们建议,未来的搜索主要序列潮汐中断使用的方法敏感的喷流辐射以及热紫外辐射。

英文摘要:

Tidal disruption of main sequence stars by black holes has generally been thought to lead to a signal dominated by UV emission. If, however, the black hole spins rapidly and the poloidal magnetic field intensity on the black hole horizon is comparable to the inner accretion disk pressure, a powerful jet may form whose luminosity can easily exceed the thermal UV luminosity. When the jet beam points at Earth, its non-thermal luminosity can dominate the emitted spectrum. The thermal and non-thermal components decay differently with time. In particular, the thermal emission should remain roughly constant for a significant time after the period of maximum accretion, beginning to diminish only after a delay, whereas after the peak accretion rate, the non-thermal jet emission decays, but then reaches a plateau. Both transitions are tied to a characteristic timescale $t_{\rm Edd}$ at which the accretion rate falls below Eddington. Making use of this timescale in a new parameter-inference formalism for tidal disruption events with significant emission from a jet, we analyze the recent flare source Swift J2058. It is consistent with an event in which a main sequence solar-type staris disrupted by a black hole of mass $\sim 4 \times 10^7 M_{\odot}$. The beginning of the flat phase in the non-thermal emission from this source can possibly be seen in the late-time lightcurve. Optical photometry over the first $\simeq 40$ d of this flare is also consistent with this picture, but is only weakly constraining because the bolometric correction is very uncertain. We suggest that future searches for main sequence tidal disruptions use methods sensitive to jet radiation as well as to thermal UV radiation.

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