The statistics of microlensing light curves – I. Amplification probability distributions

The passage of stars through the beam of a lensed quasar can induce violentfluctuations in its apparent brightness. The fluctuations observed in theHuchra lens, (2237+0305), are taken to be the first evidence of this``microlensing'' occurring in lensing systems. Subsequent microlensing eventsobserved in this system and in other gravitational lenses illustrate thatmicrolensing should be a common phenomenon in lensed quasars. The statisticalproperties of the component light curves will be defined to a large extent bythe mass distribution of the microlensing objects and the internal lightdistribution of the lensed quasar. We present statistics of a large sample ofhypothetical microlensing light curves, for a number of lensing situations,generated using an efficient numerical technique. These artificial light curvesshow that the amplification probability distributions are independent of themass function of the compact lensing objects. The amplification probabilitydistributions for the Huchra lens system are presented.