The statistics of microlensing light curves -- II. Temporal analysis

Microlensing at cosmological distances can induce violent fluctuations in the observed light curves of macrolensed quasars. In a previous publication the amplification probability distributions for a large sample of microlensing light curves were presented. This paper extends these earlier results and presents a temporal analysis for this light-curve sample. The temporal properties are explored using the first-order structure function. The results of this study show that (1) the asymptotic global curvature of the structure function depends on the macrolensing parameters σ⋆ and γ and not on the detail of the mass distribution, (2) the characteristic time-scale for variability due to microlensing is ∝, where 〈m〉 is the average mass of the microlensing objects, and again does not depend on the detailed shape of the mass distribution, and (3) the structure function time-scale does not vary with shear angle as a purely geometric transformation, but does possess an underlying symmetry solely dependent on the macrolensing parameters. A comparison of simulations of the quadruple lens, 2237 + 0305, with the currently available temporal light curves suggests that the average mass distribution of the lensing objects in 2237 + 0305 is within the range 0.1 < 〈w〉 < 10 M⊙.