A Comptonization Model for Phase-Lag Variability in GRS 1915+105

In this Letter, we propose a simple thermal Comptonization model to account for the observed properties of the phase lags associated to the "plateau" intervals of GRS 1915+105. By invoking a temperature stratification in a corona and assuming that the optical depth of the Comptonizing region increases as the disk inner radius moves inward, we are able to reproduce both the observed colors and time lags in the continuum.