We report on an investigation of the SBS 1520+530 gravitational lens system .
We have used archival HST imaging , Keck spectroscopic data , and Keck adaptive-optics imaging to study the lensing galaxy and its environment .
The AO imaging has allowed us to fix the lens galaxy properties with a high degree of accuracy when performing the lens modeling , and the data indicate that the lens has an elliptical morphology and perhaps a disk .
The new spectroscopic data suggest that previous determinations of the lens redshift may be incorrect , and we report an updated , though inconclusive , value z _ { lens } = 0.761 .
We have also spectroscopically confirmed the existence of several galaxy groups at approximately the redshift of the lens system .
We create new models of the lens system that explicitly account for the environment of the lens , and we also include improved constraints on the lensing galaxy from our adaptive-optics imaging .
Lens models created with these new data can be well-fit with a steeper than isothermal mass slope ( \alpha = 2.29 , where \rho \propto r ^ { - \alpha } ) if H _ { 0 } is fixed at 72 km s ^ { -1 } Mpc ^ { -1 } ; isothermal models require H _ { 0 } \sim 50 km s ^ { -1 } Mpc ^ { -1 } .
The steepened profile may indicate that the lens is in a transient perturbed state caused by interactions with a nearby galaxy .