Structure Function Analysis of Long-Term Quasar Variability
Structure Function Analysis of Long-Term Quasar Variability
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DOI：
10.1086/427393
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发表时间：
2004-11
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影响因子：
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通讯作者：
W. Vries;R. Becker;R. White;C. L. U. O. California;Davis;Igpp;Lawrence Livermore National Laboratory-Lawrence-Livermore-National-Labora
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文献类型：
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作者：
W. Vries;R. Becker;R. White;C. L. U. O. California;Davis;Igpp;Lawrence Livermore National Laboratory-Lawrence-Livermore-National-Labora
在我们的第二篇关于类星体长期变率的论文中，我们使用了比de弗里斯、Becker和白色中更大的类星体数据库。这个扩展的样本包含来自斯隆数字巡天（SDSS）数据发布2的35，165个类星体和来自2度场（2dF）类星体红移巡天的同一天空区域的6413个额外类星体，使我们能够显着改进我们早期的结论。和以前一样，所有历史上的类星体测光都是通过在每个类星体位置周围使用大量的校准星来校准到SDSS标度上的。我们发现：（1）爆发具有不对称的光变曲线轮廓，具有快速上升，缓慢下降的形状;这与类星体视线上的微透镜事件沿着主导类星体长期变化的假设相矛盾。(2)类星体的结构函数在20 - 40年的时间尺度内没有翻转，并且随着时间滞后的增加，变率的增加是单调和恒定的。(3)因此，类星体并没有一个单一的优选特征爆发时标，而很可能是一个连续的爆发时标。(4)类星体的变化幅度是波长的函数：光谱的蓝色部分的变化增加。(5)高光度类星体的变化小于低光度类星体，这与绝对星等变化有限的情况相一致。在此基础上，我们得出结论，类星体的变化是内在的活动星系核，是由色爆发或耀斑，有有限的光度范围，不同的时间尺度，和一个整体不对称的光变曲线形状。目前，最有希望拟合观测结果的模型是基于吸积盘不稳定性的。
In our second paper on long-term quasar variability, we employ a much larger database of quasars than in de Vries, Becker & White. This expanded sample, containing 35,165 quasars from the Sloan Digital Sky Survey (SDSS) Data Release 2 and 6413 additional quasars in the same area of the sky taken from the Two Degree Field (2dF) QSO Redshift Survey, allows us to significantly improve on our earlier conclusions. As before, all the historic quasar photometry has been calibrated onto the SDSS scale by using large numbers of calibration stars around each quasar position. We find the following: (1) The outbursts have an asymmetric light-curve profile, with a fast-rise, slow-decline shape; this argues against a scenario in which microlensing events along the line of sight to the quasars are dominating the long-term variations in quasars. (2) There is no turnover in the structure function of the quasars up to timescales of ∼40 yr, and the increase in variability with increasing time lags is monotonic and constant. (3) Consequently, there is not a single preferred characteristic outburst timescale for the quasars, but most likely a continuum of outburst timescales. (4) The magnitude of the quasar variability is a function of wavelength: variability increases toward the blue part of the spectrum. (5) High-luminosity quasars vary less than low-luminosity quasars, consistent with a scenario in which variations have limited absolute magnitude. On this basis, we conclude that quasar variability is intrinsic to the active galactic nucleus and is caused by chromatic outbursts or flares that have limited luminosity range, varying timescales, and an overall asymmetric light-curve shape. Currently, the model that has the most promise of fitting the observations is based on accretion disk instabilities.