Submillimeter Array Polarimetry with Hertz
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Abstract
We describe the characteristics of the 350 km polarimeter Hertz learned from laboratory tests and recent observations at the Caltech Submillimeter Observatory. Hertz contains a pair of 32 element arrays with 18A pixel spacing and 20A resolution. The instrument has been improved since initial observations in 1994 and 1995 ; the detector noise is now below the sky background noise. In excellent weather conditions on Mauna Kea, the noise-equivalent ux density (NEFD) for the measurement of polarized ux is 34 Jy Hz~1@2. The subtraction of correlated sky noise accomplished by the two-array design is crucial for achieving this performance. A method for analysis of our polarization data in the presence of the correlated noise is described. The instrumental polarization of Hertz is less than 0.5% across the detector array. Systematic errors in the measurement of polarization are less than 0.2%. We present a 350 km polarization map of Sgr B2 with 140 detections at greater than 3 p signicance. For our current database of all 350 km polarization measurements, the median polarization is 1.1%.
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