Thermal comptonization and disk thermal reprocessing in NGC 3516

We present an application of the thermal Comptonization/disk reprocessing m odel recently proposed by Zdziarski, Lubinski, & Smith. We show that the ab sence of strong optical variations in the presence of strong concurrent X-r ay variations, similar to those found by Hubble Space Telescope (HST)/Rossi X-Ray Timing Explorer (RXTE) monitoring observations of NGC 3516, can be e xplained by changing the geometry of the Comptonizing plasma rather than th e accretion disk itself. The total X-ray luminosity of the Comptonizing pla sma must decrease as its spatial extent increases. In contrast, the disk in ner radius must be roughly fixed in order not to produce optical/ ultraviol et color variations stronger than observed. By including emission due to in ternal viscous dissipation in the disk, we can roughly match the optical an d X-ray flux levels and variability amplitudes seen from NGC 3516 during th e HST/RXTE campaign.