Optical variability in active galactic nuclei: Starbursts or disk instabilities?
Optical variability in active galactic nuclei: Starbursts or disk instabilities?
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DOI：
10.1086/306105
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发表时间：
1998-09-10
影响因子：
4.9
通讯作者：
Turner, EL
中科院分区：
文献类型：
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作者：
Kawaguchi, T;Mineshige, S;Turner, EL
非周期性光学变率是活动星系核（AGN）的一个共同特性，尽管其物理起源仍然存在疑问。为了研究活动星系核中光紫外光变的起源，我们用结构函数分析的方法比较了两个模型的光变曲线和类星体0957 + 561的观测结果。在星暴（SB）模型中，超新星在核星暴区域的随机叠加产生非周期性的光度变化，而在盘不稳定（DI）模型中，变化是由超大质量黑洞周围吸积盘的不稳定性引起的。我们计算波动的光变曲线和结构函数，V（τ），通过简单的Monte Carlo模拟的基础上的两个模型。每个合成的V（tau）在短时间滞后（tau）处具有与tau（beta）成比例的幂律部分[V（tau）]（1/2）。这两个模型可以通过对数斜率β来区分; SB模型中的β类似于0.74-0.90，DI模型中的β类似于0.41-0.49，而观察到的光变曲线表现出类似于0.35的β。因此，我们得出结论，DI模型是优于SE模型在解释的斜率观测结构函数的情况下，0957 + 561，虽然这个对象是一个无线电响亮的对象，因此不是一个真正的公平的测试SE模型。此外，我们研究的时间不对称的光变曲线分别计算V（τ）的增亮和衰减阶段。这两个模型在一定程度上表现出相反的时间不对称趋势，尽管目前的观察时间还不足以检验这一预测。
Aperiodic optical variability is a common property of active galactic nuclei (AGNs), though its physical origin is still open to question. To study the origin of the optical-ultraviolet variability in AGNs, we compare light curves of two models to observations of quasar 0957 + 561 in terms of a structure function analysis. In the starburst (SB) model, random superposition of supernovae in the nuclear starburst region produces aperiodic luminosity variations, while in the disk-instability (DI) model, variability is caused by instabilities in the accretion disk around a supermassive black hole. We calculate fluctuating light curves and structure functions, V(tau), by simple Monte Carlo simulations on the basis of the two models. Each resultant V(tau) possesses a power-law portion, [V(tau)](1/2) proportional to tau(beta), at short time lags (tau). The two models can be distinguished by the logarithmic slope beta; beta similar to 0.74-0.90 in the SB model and beta similar to 0.41-0.49 in the DI model, while the observed light curves exhibit beta similar to 0.35. Therefore, we conclude that the DI model is favored over the SE model in explaining the slopes of the observational structure function in the case of 0957 + 561, though this object is a radio-loud object and thus is not really a fair test for the SE model. In addition, we examine the time asymmetry of the light curves by calculating V(tau) separately for the brightening and the decaying phases. The two models exhibit opposite trends of time asymmetry to some extent, although the present observation is not long enough to test this prediction.