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arXiv 1303.4837astro-ph.HE
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束缚恒星轨道和广义相对论对潮汐破裂耀斑时间行为的影响

The Impact of Bound Stellar Orbits and General Relativity on the Temporal Behavior of Tidal Disruption Flares

Lixin Dai, Andres Escala, Paolo Coppi

摘要:

我们对被大质量黑洞潮汐破坏的恒星进行了广义相对论粒子模拟。当一颗恒星在一个中等偏心率的束缚轨道而不是抛物线轨道上被破坏时,所产生的恒星碎片的时间行为发生了质的变化。碎片最初都是绑定的,在很短的时间内返回近心点-原始恒星轨道时间尺度。因此,所得到的回退速率可以比爱丁顿速率高得多。此外,如果恒星在黑洞附近被破坏,在广义相对论很重要的情况下,恒星和碎片轨道显示出广义相对论性的岁差。拱点岁差可使碎片流在经过几次轨道后自行交叉,可能导致碎片快速能量耗散。如果恒星在围绕旋转黑洞的倾斜轨道上被破坏,节点岁差会降低自相交的概率,并且圆化可能需要许多动力学时间尺度,延迟耀斑活动的开始。粒子动力学的检查表明,具有短的持续时间的准周期耀斑,产生时的潮汐流的中心通过近心,可能会发生在早期的光变曲线。后期的光变曲线可能仍然表现出幂律的行为,这是一般的磁盘吸积过程。今后调查的探测触发器应扩大到在事件进入渐近衰减阶段之前捕获这种“非标准”短期耀斑活动,因为这种活动可能对黑洞自旋等物理参数更敏感。

英文摘要:

We have carried out general relativistic particle simulations of stars tidally disrupted by massive black holes. When a star is disrupted in a bound orbit with moderate eccentricity instead of a parabolic orbit, the temporal behavior of the resulting stellar debris changes qualitatively. The debris is initially all bound, returning to pericenter in a short time ~ the original stellar orbital timescale. The resulting fallback rate can thus be much higher than the Eddington rate. Furthermore if the star is disrupted close to the hole, in a regime where general relativity is important, the stellar and debris orbits display general relativistic precession. Apsidal precession can make the debris stream cross itself after several orbits, likely leading to fast debris energy dissipation. If the star is disrupted in an inclined orbit around a spinning hole, nodal precession reduces the probability of self-intersection, and circularization may take many dynamical timescales, delaying the onset of flare activity. An examination of the particle dynamics suggests that quasi-periodic flares with short durations, produced when the center of the tidal stream passes pericenter, may occur in the early-time light curve. The late-time light curve may still show power-law behavior which is generic to disk accretion processes. The detection triggers for future surveys should be extended to capture such "non-standard" short-term flaring activity before the event enters the asymptotic decay phase, as this activity is likely to be more sensitive to physical parameters such as the black hole spin.

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