Discovery of Fourier-dependent time lags in cataclysmic variables
Discovery of Fourier-dependent time lags in cataclysmic variables
复制标题
发现灾难性变量中与傅立叶相关的时滞
DOI：
10.1093/mnras/stt347
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发表时间：
2013
影响因子：
4.8
通讯作者：
V. Dhillon
中科院分区：
文献类型：
--
作者：
S. Scaringi;S. Scaringi;E. Körding;P. J. Groot;P. Uttley;T. Marsh;C. Knigge;T. Maccarone;T. Maccarone;V. Dhillon
我们报告的第一项研究的傅立叶频率相关的相干性和相位/时间滞后在光学波长的激变变量（MV Lyr和LU Cam）显示典型的闪烁变化在白色光。使用ULTRACAM在威廉·赫歇尔望远镜上进行了观测。两个系统的光变曲线都是用SDSS滤波器u′、g′和r′同时获得的，节奏范围在0.5-2 s之间，使我们能够探测0.10 −3和0.11 Hz之间的时间频率。我们发现，u′、g′和r′光变曲线之间的相干性至少高达10−2 Hz。此外，我们检测到红色/负滞后，其中红色波段滞后于蓝色波段，处于最低观测频率。对于MV Lyr，观察到的时间滞后高达103 s，而LU Cam显示的时间滞后更大，为100 s。试图解释在X射线双星和活动星系核中观察到的红色/负滞后的机制涉及到靠近致密物体产生的光子反射到吸积盘的表面层上，其中滞后延迟只是光从发射源到反射吸积盘区域的旅行时间。虽然这可能是一个可行的解释MV Lyr中观察到的滞后，在LU Cam中观察到的滞后太大，无法解释从光盘和/或施主星星的反射。我们建议再处理的热时间尺度上的边界层光子吸积盘作为一种可能的机制来解释滞后观测到的吸积白色矮星，或反向（内-外）冲击盘内通过较冷的磁盘区域，因为它们向外移动。
We report the first study of Fourier-frequency-dependent coherence and phase/time lags at optical wavelengths of cataclysmic variables (MV Lyr and LU Cam) displaying typical flickering variability in white light. Observations were performed on the William Herschel Telescope using ULTRACAM. Light curves for both systems have been obtained with the SDSS filters u′, g′ and r′ simultaneously with cadences in the range ≈0.5–2 s, and allow us to probe temporal frequencies between ≈10−3 and ≈1 Hz. We find high levels of coherence between the u′, g′ and r′ light curves up to at least ≈10−2 Hz. Furthermore, we detect red/negative lags where the redder bands lag the bluer ones at the lowest observed frequencies. For MV Lyr time lags up to ≈3 s are observed, whilst LU Cam displays larger time lags of ≈10 s. Mechanisms which seek to explain red/negative lags observed in X-ray binaries and active galactic nuclei involve reflection of photons generated close to the compact object on to the surface layers of the accretion disc, where the lag delay is simply the light travel time from the emitting source to the reflecting accretion disc area. Although this could be a viable explanation for the lags observed in MV Lyr, the lags observed in LU Cam are too large to be explained by reflection from the disc and/or the donor star. We suggest reprocessing on the thermal time-scale of boundary layer photons on to the accretion disc as a possible mechanism to explain the lags observed in accreting white dwarfs, or reverse (inside-out) shocks within the disc travelling through cooler disc regions as they move outwards.