THE QUADRUPLE GRAVITATIONAL LENS PG-1115- TIME DELAYS AND MODELS(080 )

Optical photometry is presented for the quadruple gravitational lens P G 1115+080. A preliminary reduction of data taken from 1995 November t o 1996 June gives component C leading component B by 23.7 +/- 3.4 days and components Al and A2 by 9.4 days. A range of models has been fitt ed to the image positions, none of which gives an adequate fit. The be st-fitting and most physically plausible of these, taking the lensing galaxy and the associated group of galaxies to be singular isothermal spheres, gives a Hubble constant of 42 km s(-1) Mpc(-1) for Omega = 1, with an observational uncertainty of 14%, as computed from the B - C time delay measurement. Taking the lensing galaxy to have an approxima tely E5 isothermal mass distribution yields H-0 = 64 km s(-1) Mpc(-1), while taking the galaxy to be a point mass gives H-0 = 84 km s(-1) Mp c(-1). The former gives a particularly bad fit to the position of the lensing galaxy, while the latter is inconsistent with measurements of nearby galaxy rotation curves. Constraints on these and other possible models are expected to improve with planned Hubble Space Telescope ob servations.