Estimation of multiple time delays in complex gravitational lens systems

We generalize the nonparametric dispersion minimization method of time delay estimation for the case when more than two quasar images are available. This allows us to analyse time delays in complex gravitational lens systems in a model independent manner. We apply the new method to the recent observations of the quadruply imaged quasar PG 1115+080 and show that our nonparametric estimates roughly coincide with the values obtained with optimal filtering and smoothing techniques. Because our method uses a minimal set of assumptions and is computationally simpler it may be a method of choice, especially for the early stages of an investigation when the available data for a new lens system are scarce.