A MEASUREMENT OF THE MEDIUM-SCALE ANISOTROPY IN THE COSMIC MICROWAVE BACKGROUND-RADIATION

Observations from the first flight of the Medium Scale Anisotropy Meas urement (MSAM) are analyzed to place limits on Gaussian fluctuations i n the cosmic microwave background radiation (CMBR). This instrument ch ops a 30' beam in a three-position pattern with a throw of +/-40'; the resulting data is analyzed in statistically independent single- and d ouble-difference data sets. We observe in four spectral channels at 5. 6, 9.0, 16.5, and 22.5 cm-1, allowing the separation of interstellar d ust emission from CMBR fluctuations. The dust component is correlated with the IRAS 100 mum map. The CMBR component has two regions where th e signature of an unresolved source is seen. Rejecting these two sourc e regions, we obtain a detection of fluctuations which match CMBR in o ur spectral bands of 0.6 x 10(-5) < DELTAT/T < 2.2 x 10(-5) (90% CL in terval) for total rms Gaussian fluctuations with correlation angle 0.5 -degrees, using the single-difference demodulation. For the double dif ference demodulation, the result is 1.1 x 10(-5) < DELTAT/T < 3.1 x 10 (-5) (90% CL interval) at a correlation angle of 0.3-degrees.