The Time Delay of Gravitational Lens 0957+561. I. Methodology and Analysis of Optical Photometric Data

When a data set's underlying covariance function (autocorrelation) can be estimated, one can construct from the data set a global χ 2 statistic that takes into account the expected statistical relationship between all pairs of points. Incorporating a projection operator, the statistic is independent of the underlying process' mean and total variance, which are poorly determined (or ill-defined) for low-frequency divergent signals