Constraints on the temperature inhomogeneity in quasar accretion discs from the ultraviolet-optical spectral variability
Constraints on the temperature inhomogeneity in quasar accretion discs from the ultraviolet-optical spectral variability
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DOI：
10.1093/mnras/stv241
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发表时间：
2015-02
影响因子：
4.8
通讯作者：
M. Kokubo
中科院分区：
文献类型：
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作者：
M. Kokubo
类星体紫外光变的物理机制虽然有着悠久的观测历史，但人们对紫外光变的物理机制还没有很好的理解。最近，Dexter和Agol提出了一个类星体紫外光变率模型，该模型假设类星体吸积盘中存在大的局部温度波动。这种非均匀吸积盘模型不仅能描述单波段的光变幅度，而且能描述微透镜的大小约束和类星体的复合光谱形状。利用Sloan数字巡天（SDSS）Stripe 82区域近9000个类星体的五波段多历元光变曲线，研究了类星体紫外光谱变化对非均匀吸积盘模型的影响。通过比较SDSS类星体光变曲线和模拟光变曲线的两波段星等-星等图的内禀散射值，我们发现Dexter & Agol的非均匀吸积盘模型不能解释SDSS类星体光变曲线中经常观察到的紧密的带间关联.这一结果使我们得出结论，在吸积盘的局部温度波动不是类星体的几年的紫外-光学变化的主要驱动力，因此，假设类星体吸积盘有大的局部温度波动是不可取的紫外-光学光谱变化的观点。
The physical mechanisms of the quasar ultraviolet (UV)-optical variability are not well understood despite the long history of observations. Recently, Dexter & Agol presented a model of quasar UV-optical variability, which assumes large local temperature fluctuations in the quasar accretion discs. This inhomogeneous accretion disc model is claimed to describe not only the single-band variability amplitude, but also microlensing size constraints and the quasar composite spectral shape. In this work, we examine the validity of the inhomogeneous accretion disc model in the light of quasar UV-optical spectral variability by using five-band multi-epoch light curves for nearly 9 000 quasars in the Sloan Digital Sky Survey (SDSS) Stripe 82 region. By comparing the values of the intrinsic scatter $\sigma_{\text{int}}$ of the two-band magnitude-magnitude plots for the SDSS quasar light curves and for the simulated light curves, we show that Dexter & Agol's inhomogeneous accretion disc model cannot explain the tight inter-band correlation often observed in the SDSS quasar light curves. This result leads us to conclude that the local temperature fluctuations in the accretion discs are not the main driver of the several years' UV-optical variability of quasars, and consequently, that the assumption that the quasar accretion discs have large localized temperature fluctuations is not preferred from the viewpoint of the UV-optical spectral variability.