CALIBRATION AND SYSTEMATIC-ERROR ANALYSIS FOR THE COBE(1) DMR 4 YEAR SKY MAPS

The Differential Microwave Radiometers (DMR) instrument aboard the Cos mic Background Explorer (COBE) has mapped the full microwave sky to me an sensitivity 26 mu K per 7 degrees held of view. The absolute calibr ation is determined to 0.7% with drifts smaller than 0.2% per year. We have analyzed both the raw differential data and the pixelized sky ma ps for evidence of contaminating sources such as solar system foregrou nds, instrumental susceptibilities, and artifacts from data recovery a nd processing. Most systematic effects couple only weakly to the sky m aps. The largest uncertainties in the maps result from the instrument susceptibility to Earth's magnetic held, microwave emission from Earth , and upper limits to potential effects at the spacecraft spin period. Systematic effects in the maps are small compared to either the noise or the celestial signal: the 95% confidence upper limit for the pixel -pixel rms from all identified systematics is less than 6 mu K in the worst channel. A power spectrum analysis of the (A-B)/2 difference map s shows no evidence for additional undetected systematic effects.