A search for primordial anisotropies in the cosmic microwave background radiation: first observations at 13.5 GHz with the Cosmic Anisotropy Telescope

We report the first observations of the cosmic microwave background radiation (CMBR) at 13.5 GHz made with the Cosmic Anisotropy Telescope (CAT) near Cambridge. After removal of foreground radio sources brighter than 10 mJy, using the Ryle Telescope (RT), the map shows evidence for residual structure on a scale of approximately 1/2 deg with an rms variation of 18 mJy. We intend to use multifrequency measurements to distinguish between Galactic and CMBR components.