THE COLOR VARIABILITY OF QUASARS
THE COLOR VARIABILITY OF QUASARS
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DOI：
10.1088/0004-637x/744/2/147
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发表时间：
2011-09
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通讯作者：
K. Schmidt;H. Rix;J. Shields;M. Knecht;D. Hogg;D. Maoz;J. Bovy
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作者：
K. Schmidt;H. Rix;J. Shields;M. Knecht;D. Hogg;D. Maoz;J. Bovy
我们量化类星体的颜色变化，使用前所未有的变化数据库-Ugriz测光的9093类星体从斯隆数字巡天（SDSS）条纹82，观察超过8年，在1060个历元。我们证实了以前的报告，类星体变亮时变得更蓝。我们在给定的一组波段中发现了这种蓝化的红移依赖性（例如，g和r），但表明这是不同红移处不同SDSS带中较小变化或延迟发射线的通量贡献的结果。在修正了这种效应之后，类星体的颜色变化非常均匀，不仅与红移无关，而且与类星体的光度和黑洞质量无关。单个类星体的颜色变化，因为它们在一年的时间尺度上的亮度变化，比在亮度上跨越许多数量级的类星体样本中看到的颜色范围要明显得多。这表明类星体变化背后的不同物理机制，以及在给定黑洞质量下观测到的类星体光度范围-类星体变化不能用平均吸积率的变化来解释。我们确实发现了颜色变化对通量变化本身特性的一些依赖性，快速，低幅度，亮度变化产生更多的颜色变化。如果类星体的变化是由耀斑或吸积盘中短暂的热点引起的，那么观察到的行为就可能出现。
We quantify quasar color variability using an unprecedented variability database—ugriz photometry of 9093 quasars from Sloan Digital Sky Survey (SDSS) Stripe 82, observed over 8 years at ∼60 epochs each. We confirm previous reports that quasars become bluer when brightening. We find a redshift dependence of this blueing in a given set of bands (e.g., g and r), but show that it is the result of the flux contribution from less-variable or delayed emission lines in the different SDSS bands at different redshifts. After correcting for this effect, quasar color variability is remarkably uniform, and independent not only of redshift, but also of quasar luminosity and black hole mass. The color variations of individual quasars, as they vary in brightness on year timescales, are much more pronounced than the ranges in color seen in samples of quasars across many orders of magnitude in luminosity. This indicates distinct physical mechanisms behind quasar variability and the observed range of quasar luminosities at a given black hole mass—quasar variations cannot be explained by changes in the mean accretion rate. We do find some dependence of the color variability on the characteristics of the flux variations themselves, with fast, low-amplitude, brightness variations producing more color variability. The observed behavior could arise if quasar variability results from flares or ephemeral hot spots in an accretion disk.