Cosmic Microwave Background Maps from the HACME Experiment

We present Cosmic Microwave Background (CMB) maps from the Santa BarbaraHACME balloon experiment (Staren etal 2000), covering about 1150 square degreessplit between two regions in the northern sky, near the stars gamma UrsaeMinoris and alpha Leonis, respectively. The FWHM of the beam is about 0.77degrees in three frequency bands centered on 39, 41 and 43 GHz. The resultsdemonstrate that the thoroughly interconnected scan strategy employed allowsefficient removal of 1/f-noise and slightly variable scan-synchronous offsets.The maps display no striping, and the noise correlations are found to bevirtually isotropic, decaying on an angular scale around one degree. The noiseperformance of the experiment resulted in an upper limit on CMB anisotropy.However, our results demonstrate that atmospheric contamination and othersystematics resulting from the circular scanning strategy can be accuratelycontrolled, and bodes well for the planned follow-up experiments BEAST and ACE,since they show that even with the overly cautious assumption that 1/f-noiseand offsets will be as dominant as for HACME, the problems they pose can bereadily overcome with the mapmaking algorithm discussed. Our prewhitenednotch-filter algorithm for destriping and offset removal should be useful alsofor other balloon- and ground-based experiments whose scan strategies involvesubstantial interleaving.