ANISOTROPY IN THE MICROWAVE SKY AT INTERMEDIATE ANGULAR SCALES

Observations of a low-background region of sky at high Galactic latitude in a frequency band centered at nu = 90 GHz reveal highly significant detections of anisotropy on intermediate (approximately 1-degrees) angular scales. The instrument is a 2 x 2 array of bolometric detectors operating at 50 mK, coupled to a 0.75 m off-axis parabolic telescope by single mode corrugated feedhorns. The FWHM beamwidth of the instrument is 0.75-degrees, with a beamswitch of +/-2.75-degrees on the sky. Interpreting the detected fluctuations as due to anisotropy in the cosmic microwave background, a likelihood analysis assuming a Gaussian correlation function in the temperature fluctuations yields most likely values of DELTAT/T of 3.1(+2.5/-0.9) x 10(-5) and 3.8(+2.9/-1.2) X 10(-5) at a coherence angle of 1.0-degrees, for the left- and right-hand detectors, respectively. The stated errors are 95% confidence limits. Confirmation at other frequencies is required to rule out the possibility of foreground contamination.