A DEGREE SCALE ANISOTROPY MEASUREMENT OF THE COSMIC MICROWAVE BACKGROUND NEAR THE STAR GAMMA-URSAE-MINORIS

Results from a search for anisotropy in the cosmic microwave backgroun d (CMB) are presented from the third flight of the Millimeter-wave Ani sotropy eXperiment. Observations were made at 6, 9, and 12 cm-1 with a 0-degrees-5 FWHM beam and a 1-degrees-3 sinusoidal chop. The CMB obse rvation occurred over 1.37 hours and covered a 6.24 deg2 area of the s ky where very little foreground emission is expected. Significant corr elated structure is observed at 6 and 9 cm-1. At 12 cm-1 we place an u pper limit on the structure. The relative amplitudes at 6, 9, and 12 c m-1 are consistent with a CMB spectrum. The spectrum of the structure is inconsistent with thermal emission from known forms of interstellar dust. Synchrotron and free-free emission would both require unusually flat spectral indices at cm wavelengths in order to account for the a mplitude of the observed structure. Although known systematic errors a re not expected to contribute significantly to any of the three optica l channels, excess sidelobe contamination cannot be definitively ruled out. If all the structure is attributed to CMB anisotropy, a value of the weighted rms of the 6 and 9 cm-1 channels of AT(rms)/T(CMB) = 4.7 +/- 0.8 x 10(-5) (+/-1 sigma) was measured. If the CMB anisotropy is assumed to have a Gaussian autocorrelation function with a coherence a ngle of 25', then the most probable value is AT(rms)/T(CMB) = 4.2-1.1( +1.7) x 10(-5) where the +/- refers to the 95% confidence limits. Thes e values are similar to a measurement made in the same region of the s ky on a previous flight; however, this lower limit is larger than the upper limit that was obtained in a different region of the sky during the same flight.