Analyzing the Flux Anomalies of the Large-separation Lensed Quasar SDSS J1029+2623

Using a high-resolution radio image, we successfully resolve the two-fold image components B and C of the quasar lens system SDSS J1029+2623. The flux anomalies associated with these two components in the optical regime persist, albeit less strongly, in our radio observations suggesting that the cluster must be modeled by something more than a single central potential. We argue that placing substructure close to one of the components can account for a flux anomaly with negligible changes in the component positions. Our best-fit model has a substructure mass of ~10⁹ M _sun up to the mass-sheet degeneracy, located roughly 0farcs1 west and 0farcs1 north of component B. We demonstrate that a positional offset between the centers of the source components can explain the differences between the optical and radio flux ratios.