Implications from Late-time X-Ray Detections of Optically Selected Tidal Disruption Events: State Changes, Unification, and Detection Rates
Implications from Late-time X-Ray Detections of Optically Selected Tidal Disruption Events: State Changes, Unification, and Detection Rates
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DOI：
10.3847/1538-4357/ab659c
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发表时间：
2019-06
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影响因子：
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通讯作者：
P. Jonker;N. Stone;A. Generozov;S. Velzen;B. Metzger
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文献类型：
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作者：
P. Jonker;N. Stone;A. Generozov;S. Velzen;B. Metzger
我们给出了四个光学选择的潮汐破裂事件(TDEs)的Chandra X射线观测，这些事件是在发现4-9年后获得的。探测到三个发光强度在9×1040~3×1042erg S−1之间的光源。PtF09AXc的光谱符合指数2.5±0.1的幂定律，而PtF09Ge的光谱很软。PTF09axc的幂律谱和以前的文献发现提供了证据，证明TDEs在中断多年后从早期的软态转变为晚期的硬态。我们认为，光学发射和X射线发射达到峰值的时间可能在TDEs中有很大不同，X射线产生或变得可观察到的时间较晚。这种延迟有助于解释观察到的性质的不同，如光学和X射线选择的TDEs的lopt/lx。我们更新了eROSITA仪器的TDE速率预测：它的范围从3年到990年−1，这敏感地取决于黑洞自旋的分布以及从破裂到峰值X射线亮度之间的时间延迟。我们进一步预测，在光学和X射线选择的TDEs样本中，退行性和进行性椎间盘的数量是不对称的。观测偏差的细节可能有助于观察到光学和X射线选择的TDEs之间的差异(对于逆行TDE盘，光学选择的TDEs在X射线中较弱)。
We present Chandra X-ray observations of four optically selected tidal disruption events (TDEs) obtained 4–9 yr after discovery. Three sources were detected with luminosities between 9 × 1040 and 3 × 1042 erg s−1. The spectrum of PTF09axc is consistent with a power law of index 2.5 ± 0.1, whereas the spectrum of PTF09ge is very soft. The power-law spectrum of PTF09axc and prior literature findings provide evidence that TDEs transition from an early-time soft state to a late-time hard state many years after disruption. We propose that the time to peak luminosity for optical and X-ray emission may differ substantially in TDEs, with X-rays being produced or becoming observable later. This delay helps explain the differences in observed properties such as Lopt/LX of optically and X-ray-selected TDEs. We update TDE rate predictions for the eROSITA instrument: it ranges from 3 to 990 yr−1, depending sensitively on the distribution of black hole spins and the time delay between disruption and peak X-ray brightness. We further predict an asymmetry in the number of retrograde and prograde disks in samples of optically and X-ray-selected TDEs. The details of the observational biases can contribute to observed differences between optically and X-ray-selected TDEs (with optically selected TDEs being fainter in X-rays for retrograde TDE disks).