A reassessment of the data and models of the gravitational lens Q0957+561

We examine models of the mass distribution for the first known case of grav itational lensing. Several new sets of constraints are used, based on recen t observations. We remodel the VLBI observations of the radio cores and jet s in the two images of Q0957 + 561, showing that the previously derived pos itions and uncertainties were incorrect. We use as additional constraints t he candidate lensed pairs of galaxies discovered recently with the Hubble S pace Telescope. We explore a wider range of lens models than before and fin d that the Hubble constant is not tightly constrained once elliptical lens models are considered. We also discuss the systematic uncertainties caused by the cluster containing the lens galaxy. We conclude that additional obse rvations of the candidate lensed galaxies as well as direct measurements of the cluster mass profile are needed before a useful value of the Hubble co nstant can be derived from this lens.