A measurement of H0 from Ryle Telescope, ASCA and ROSAT observations of Abell 773

We present new Ryle Telescope (RT) observations of the Sunyaev–Zel'dovich (SZ) decrement from the cluster Abell 773. The field contains a number of faint radio sources that required careful subtraction. We use ASCA observations to measure the gas temperature and a ROSAT HRI image to model the gas density distribution. Normalizing the gas distribution to fit the RT visibilities returns a value of H0 of 77+19−15 km s−1 Mpc−1 (1σ errors) for an Einstein–de Sitter universe, or 85+20−17 km s−1 Mpc−1 for a flat model with ΩΛ= 0.7. The errors quoted include estimates of the effects of the principal errors: noise in the SZ measurement, gas temperature uncertainty and line-of-sight depth uncertainty.