A Measurement of the Cosmic Microwave Background Temperature at 1280 Mhz

The absolute temperature of the cosmic microwave background (CMB) has been measured at a frequency of 1280 MHz. The observation was made with a modified version of the L-band receiver used in the Giant Metre wavelength Radio Telescope (GMRT): the feed horn was replaced by a corrugated plate and the receiver was placed on the ground, directed at zenith, and shielded from ground radiation by an aluminium screen with corrugated edges. Novel techniques have been adopted for (1) reducing and cancelling unwanted contributions to the system temperature of the receiver and (2) calibrating the contributions from the feed assembly and receiver. The thermodynamic temperature of the CMB is estimated to be 3.45 ± 0.78 K.