MSAM1-94: Repeated Measurement of Medium-Scale Anisotropy in the Cosmic Microwave Background Radiation

The second flight of the Medium Scale Anisotropy Measurement (MSAM194) observed the same field as the first flight (MSAM1-92) to confirm our earlier measurement of cosmic microwave background radiation (CMBR) anisotropy. This instrument chops a 30 beam in a 3 position pattern with a throw of ±40′, and simultaneously measures single and double differenced sky signals. We observe in four spectral channels centered at 5.6, 9.0, 16.5, and 22.5 cm, providing sensitivity to the peak of the CMBR and to thermal emission from interstellar dust. The dust component correlates well with the IRAS 100 μm map. The CMBR observations in our double difference channel correlate well with the earlier observations, but the single difference channel shows some discrepancies. We obtain a detection of fluctuations in the MSAM1-94 dataset that match CMBR in our spectral bands of ∆T/T = 1.9 −0.7 × 10 (90% confidence interval, including calibration uncertainty) for total rms Gaussian fluctuations with correlation angle 0. 3, using the double difference demodulation. Subject headings: balloons — cosmic microwave background — cosmology: observations NASA/Goddard Space Flight Center, Laboratory for Astronomy and Solar Physics, Code 685.0, Greenbelt, MD 20771 Global Science and Technology, Inc., NASA/GSFC Laboratory for Astronomy and Solar Physics, Code 685.0, Greenbelt, MD 20771 Applied Research Corporation, NASA/GSFC Laboratory for Astronomy and Solar Physics, Code 685.3, Greenbelt, MD 20771 University of Chicago, 5640 S. Ellis St., Chicago, IL 60637 Princeton University Physics Dept., Princeton, NJ 08544