the core image coordinates contributed $2-3$ times more to $\chi^2$ than for the original parameter values in models A-D. Thus, we are unable to account in detail for the full set of measured properties of the images of the core.

Although we did not include them as constraints to our fits, we are able to account qualitatively for the arcs. Figure 8 shows the image and source planes for model C, with simulated source components: the four QSO images are produced by a single compact source inside the astroid caustic, and the arc is produced by an extended source that lies just inside the caustic. In VLBI observations (PP96), extended radio emission (roughly aligned with the arc emanating from B) is apparent near image B, with no counterpart near images A1 and A2. Such a configuration is consistent with the source of extended radio emission being just outside the caustic (see Figure 8).

The arc and the images of the core share geometric properties (the separation of the arc and core sources is $\sim 200 h^{-1}$ pc, according to our model C), but their measured colors are dissimilar. Their mean radial distance from the center of G is $1\farcs2 \pm 