core; (6) a possible new test to distinguish between reddening in the host galaxy of the QSO and in the lens galaxy, based on future accurate measurements of spatial variations in the color of the arc; and (7) the suggestion that microlensing is a plausible cause for the differences between the radio and optical flux ratios for the brightest images, A1 and A2. Further observations and measurements such as of the redshift of the lens galaxy, can be used fruitfully to study microlensing for this system.'
author:
- 'Emilio E. Falco, Joseph Lehár, and Irwin I. Shapiro'
title: HST Observations and Models of The Gravitational Lens System 
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Introduction
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Among the most spectacular examples of gravitational lensing by isolated galaxies are the quadruple systems of images, with characteristic sizes of a few arcseconds.  (hereafter ) was discovered by the MG radio survey (see, e.g., Hewitt   1989), because of its distinctive “quad” radio morphology (Hewitt   1992, hereafter HTLSB92). The image configuration is the “classic” bright, close double (A1 and A2 separated by $0\farcs4$) assumed to straddle a critical curve, plus two additional, fainter images (B and C, each $\sim 2''$ from A1 and A2 and from each other). The redshift 