An Absolute Measurement of the Cosmic Microwave Background Radiation Temperature at 10.7 GH[CLC]z[/CLC]

A balloon-borne experiment has measured the absolute temperature of thecosmic microwave background radiation (CMBR) at 10.7 GHz to be Tcmbr = 2.730 +-.014 K. The error is the quadratic sum of several systematic errors, withstatistical error of less than 0.1 mK. The instrument comprises a cooledcorrugated horn antenna coupled to a total-power radiometer. A cryogenicmechanical waveguide switch alternately connects the radiometer to the horn andto an internal reference load. The small measured temperature difference (<= 20mK) between the sky signal and the reference load in conjunction with the useof a cold front end keeps systematic instrumental corrections small.Atmospheric and window emission are minimized by flying the instrument at 24 kmaltitude. A large outer ground screen and smaller inner screen shield theinstrument from stray radiation from the ground and the balloon. In-flighttests constrain the magnitude of ground radiation contamination, and low levelinterference is monitored through observations in several narrow frequencybands.Comment: 14 pages, 1 figure, submitted to ApJ