Detection of the Sunyaev-Zel'dovich effect in Abell 773

We have observed the cluster Abell 773 with the Ryle Telescope at 15 GHz, and have measured a decrement in the cosmic microwave background radiation (CMB) of $$-590 \pm 116 \mu\enspace \text {Jy}\enspace \text {beam}^{-1}$$, due to the Sunyaev- Zel'dovich (S–Z) effect. On reasonable assumptions about the structure of the cluster atmosphere, this implies a central temperature decrement of between –790 and –990 μK. Together with the previous detection in A2218, which is significantly different from A773 as regards radiosource confusion, this result confirms the power of the method used, and emphasizes the advantages of interferometric methods over switched-beam telescopes for imaging structure in the CMB.