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The UV emission from X-ray binaries, is more likely to be produced byreprocessing of X-rays by the outer regions of an accretion disk. The structureof the outer disk may be altered due to the presence of X-ray irradiation andwe discuss the physical regimes where this may occur and point out certainX-ray binaries where this effect may be important. The long term X-rayvariability of these sources is believed to be due to stochastic fluctuationsin the outer disk, which propagate inwards giving rise to accretion ratevariation in the X-ray producing inner regions. The X-ray variability willinduce structural variations in the outer disk which in turn may affect theinner accretion rate. To understand the qualitative behaviour of the disk insuch a scenario, we adopt simplistic assumptions that the disk is fully ionisedand is not warped. We develop and use a time dependent global hydrodynamicalcode to study the effect of a sinusoidal accretion rate perturbation introducedat a specific radius. The response of the disk, especially the inner accretionrate, to such perturbations at different radii and with different time periodsis shown. While we didn't find any oscillatory or limit cycle behaviour, ourresults show that irradiation enhances the X-ray variability at time-scalescorresponding to the viscous time-scales of the irradiated disk.

The Effect of X-ray Irradiation on the Time Dependent Behaviour of Accretion Disks with Stochastic Perturbations