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We fit outbursts of two X-ray novae (Nova Monocerotis 1975=A0620-00 and NovaMuscae GS 1991=1124-683) using a time-dependent accretion disk model. The modelis based on a new solution for a diffusion-type equation for thenon-steady-state accretion and describes the evolution of a viscous alpha-diskin a binary system after the peak of an outburst, when matter in the disk istotally ionized. The accretion rate in the disk decreases according to a powerlaw. We derive formulas for the accretion rate and effective temperature of thedisk. The model has three free input parameters: the mass of the central objectM, the turbulence parameter alpha, and the normalization parameter delta t.Results of the modeling are compared with the observed X-ray and optical B andV light curves. The resulting estimates for the turbulence parameter $\alpha$are similar: 0.2-0.4 for A 0620-00 and 0.45-0.65 for GS 1124-683, suggesting asimilar nature for the viscosity in the accretion disks around the compactobjects in these sources. We also derive the distances to these systems asfunctions of the masses of their compact objects.

Non-Steady State Accretion Disks in X-Ray Novae: Outburst Models for Nova Monocerotis 1975 and Nova Muscae 1991