Late-time UV Observations of Tidal Disruption Flares Reveal Unobscured, Compact Accretion Disks
Late-time UV Observations of Tidal Disruption Flares Reveal Unobscured, Compact Accretion Disks
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潮汐瓦解耀斑的最新紫外线观测揭示了清晰、紧凑的吸积盘
DOI：
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发表时间：
2018
影响因子：
4.9
通讯作者：
A. Fruchter
中科院分区：
文献类型：
--
作者：
Sanne G M van Velzen;N. Stone;B. Metzger;S. Gezari;T. Brown;A. Fruchter
恒星潮汐爆发耀斑(TDF)的热辐射、光学辐射和紫外线辐射的来源仍然是一个悬而未决的问题。我们介绍了哈勃太空望远镜对8个光学/UV选择的TDF的5-10年后的远紫外光(FUV)观测。六个源被干净地探测到，显示出它们所在星系中心发出的点状FUV辐射()。我们发现，来自低质量黑洞(<；106.5 M⊙)的TDF的光曲线表现出明显的后期平坦化。相反，来自高质量黑洞TDF的FUV光曲线通常与从早期光曲线外推得到的一致。观测到的晚期辐射不能用现有的早期TDF光曲线模型(即，后处理或环化激波)来解释，而是与粘性扩散的、未被遮挡的吸积盘相一致。然而，与α圆盘理论最简单的预测相反，这些圆盘模型只有在假设它们是热和粘性稳定的情况下才能再现观测到的全紫外光亮度。对于我们样本中的一个TDF，我们测量了UV光度的上限，该上限明显低于理论建模和对早期光曲线的外推。这种后期发射的缺乏可能是由于样品的其余部分没有磁盘不稳定/状态变化。解释后期紫外线探测的圆盘模型通过在几十年内辐射∼0.1M⊙的静止质量能量，主要是在极端紫外线波长下辐射，解决了TDF“缺失能量问题”。
The origin of thermal optical and UV emission from stellar tidal disruption flares (TDFs) remains an open question. We present Hubble Space Telescope far-UV (FUV) observations of eight optical/UV-selected TDFs 5–10 yr post-peak. Six sources are cleanly detected, showing point-like FUV emission ( ) from the centers of their host galaxies. We discover that the light curves of TDFs from low-mass black holes (<106.5 M⊙) show significant late-time flattening. Conversely, FUV light curves from high-mass black hole TDFs are generally consistent with an extrapolation from the early-time light curve. The observed late-time emission cannot be explained by existing models for early-time TDF light curves (i.e., reprocessing or circularization shocks), but is instead consistent with a viscously spreading, unobscured accretion disk. These disk models can only reproduce the observed FUV luminosities, however, if they are assumed to be thermally and viscously stable, in contrast to the simplest predictions of α-disk theory. For one TDF in our sample, we measure an upper limit to the UV luminosity that is significantly lower than expectations from theoretical modeling and an extrapolation of the early-time light curve. This dearth of late-time emission could be due to a disk instability/state change absent in the rest of the sample. The disk models that explain the late-time UV detections solve the TDF “missing energy problem” by radiating a rest-mass energy of ∼0.1 M⊙ over a period of decades, primarily in extreme UV wavelengths.
DOI：
10.3847/2041-8213/aab429
发表时间：
2018-03
期刊：
The Astrophysical Journal Letters
影响因子：
--
作者：
L. Dai;L. Dai;J. McKinney;Nathaniel Roth;E. Ramirez-Ruiz;E. Ramirez-Ruiz;M. Miller
通讯作者：
L. Dai;L. Dai;J. McKinney;Nathaniel Roth;E. Ramirez-Ruiz;E. Ramirez-Ruiz;M. Miller
影响因子：
4.8
作者：
J. Bright;R. Fender;S. Motta;K. Mooley;Y. Perrott;S. Velzen;S. Carey;J. Hickish;N. Razavi-Ghods;D. Titterington;P. Scott;K. Grainge;A. Scaife;T. Cantwell;C. Physics;U. Oxford;Oxford;UK.;A. Group;C. Laboratory;Cambridge;D. Physics;Astronomy;T. J. H. University;Baltimore.;Usa;J. B. C. F. Astrophysics;U. Manchester;Manchester
通讯作者：
J. Bright;R. Fender;S. Motta;K. Mooley;Y. Perrott;S. Velzen;S. Carey;J. Hickish;N. Razavi-Ghods;D. Titterington;P. Scott;K. Grainge;A. Scaife;T. Cantwell;C. Physics;U. Oxford;Oxford;UK.;A. Group;C. Laboratory;Cambridge;D. Physics;Astronomy;T. J. H. University;Baltimore.;Usa;J. B. C. F. Astrophysics;U. Manchester;Manchester