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arXiv 2207.07136astro-ph.HE
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潮汐中断事件的冷却包线模型

Cooling Envelope Model for Tidal Disruption Events

Brian D. Metzger

摘要:

我们提出了一个玩具模型的热光学/紫外/X射线辐射的潮汐破坏事件(TDE)。受最近流体动力学模拟的启发,我们假设碎片流迅速地(在最紧密结合的碎片的轨道周期上)循环,产生一个围绕超大质量黑洞(SMBH)的半径为R_v ~ 1 e14 cm(光球半径~ 1 e15 cm)的热的准球形压力支持包层。当包层辐射冷却时,它经历开尔文-亥姆霍兹收缩R_v ~ t^(-1),温度升高T_eff ~ t^(1/2),而总光度大致保持不变;光学光度衰减为nu L_nu ~ R_v^2 T_eff ~ t^(-3/2)。尽管与质量回落速率Mdot_fb ~ t^(-5/3)相似,但与包层冷却光度相比,来自回落吸积的包层加热是次主导的,除了在光学峰值附近(在那里它们是可比的)。包层收缩可以通过从内包层到SMBH上的吸积能量注入以调节的方式延迟,导致光学/X射线光变曲线的后期平坦化,类似于在一些TDE中观察到的。最后,当包层收缩到接近圆化半径时,SMBH吸积率上升到最大值,同时光学光度下降。这种冷却引起的(而不是循环引起的)长达几百天的延迟,可以解释在一些TDE中观察到的热X射线,晚期射电耀斑和高能中微子产生的延迟。我们将模型预测与最近的TDE光变曲线相关性研究进行了比较,发现了一致性和紧张点。

英文摘要:

We present a toy model for the thermal optical/UV/X-ray emission from tidal disruption events (TDE). Motivated by recent hydrodynamical simulations, we assume the debris streams promptly and rapidly circularize (on the orbital period of the most tightly bound debris), generating a hot quasi-spherical pressure-supported envelope of radius R_v ~ 1e14 cm (photosphere radius ~1e15 cm) surrounding the supermassive black hole (SMBH). As the envelope cools radiatively, it undergoes Kelvin-Helmholtz contraction R_v ~ t^(-1), its temperature rising T_eff ~ t^(1/2) while its total luminosity remains roughly constant; the optical luminosity decays as nu L_nu ~ R_v^2 T_eff ~ t^(-3/2). Despite this similarity to the mass fall-back rate Mdot_fb ~ t^(-5/3), envelope heating from fall-back accretion is sub-dominant compared to the envelope cooling luminosity except near optical peak (where they are comparable). Envelope contraction can be delayed by energy injection from accretion from the inner envelope onto the SMBH in a regulated manner, leading to a late-time flattening of the optical/X-ray light curves, similar to those observed in some TDEs. Eventually, as the envelope contracts to near the circularization radius, the SMBH accretion rate rises to its maximum, in tandem with the decreasing optical luminosity. This cooling-induced (rather than circularization-induced) delay of up to several hundred days, may account for the delayed onset of thermal X-rays, late-time radio flares, and high-energy neutrino generation, observed in some TDEs. We compare the model predictions to recent TDE light curve correlation studies, finding agreement as well as points of tension.

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