Inhomogeneous Disk Structure

So far we assumed a homogeneous, steady disk structure. However, the most striking feature of quasar light lies in its rapid variability. Probably, such variation is caused by local, transient brightening or flares. We then expect rather inhomogeneous disk structure full of blobs, spots, or filaments, if viewed with X-rays from its vicinity (just like the X-ray image of the Sun). Recently performed three-dimensional (3D) magnetohydrodynamical (MHD) simulations also support this view (Machida, Hayashi, & Matsumoto 2000).

Figure 2: Microlens light curves of a disk with multiple blobs. The thick dashed line represents the case with no blobs, and the two solid lines represent the cases with 3 (model A) and 12 blobs (model B).

To demonstrate such effects, we perform simple calculations; we put 3 (model A) or 12 blobs (model B) on a disk with flat brightness distribution. The resultant light variations are plotted in Figure 2 in comparison with the case with no blobs (by the dashed line). Although the total blob luminosity is only 20% of the total in this model, microlens light variations record dramatic changes. In reality, moreover, positions and luminosities of blobs are likely to be time-varying, creating more complex variations. We may be able to obtain informations regarding the site and emission processes of the intrinsic variability, when densely sampled microlens light curves at various wavelengths are available. More details will be published elsewhere (Takahashi, Yonehara, & Mineshige 2001).

б© Copyright Astronomical Society of Australia 1997