We discuss a systematic effect associated with measuring polarization with a continuously rotating half-wave plate (HWP). The effect was identified with the data from the E and B Experiment, which was a balloon-borne instrument designed to measure the polarization of the cosmic microwave background (CMB) as well as that from Galactic dust. The data show polarization fractions larger than 10%, while less than 3% were expected from instrumental polarization. We give evidence that the excess polarization is due to detector nonlinearity in the presence of a continuously rotating HWP. The nonlinearity couples intensity signals to polarization. We develop a map-based method to remove the excess polarization. Applying this method to the 150 (250) GHz band data, we find that 81% (92%) of the excess polarization was removed. Characterization and mitigation of this effect are important for future experiments aiming to measure the CMB B-modes with a continuously rotating HWP.
Intensity-coupled Polarization in Instruments with a Continuously Rotating Half-wave Plate / Didier, J., Miller, A.D., Araujo, D., Aubin, F., Geach, C., Johnson, B., Korotkov, A., Raach, K., Westbrook, B., Young, K., Aboobaker, A.M., Ade, P., Baccigalupi, C., Bao, C., Chapman, D., Dobbs, M., Grainger, W., Hanany, S., Helson, K., Hillbrand, S., et al.. - In: THE ASTROPHYSICAL JOURNAL. - ISSN 0004-637X. - 876:1(2019), pp. 1-14. [10.3847/1538-4357/ab0f36]
Intensity-coupled Polarization in Instruments with a Continuously Rotating Half-wave Plate
Baccigalupi, C.;Jaffe, A.;Lee, A.;Limon, M.;Pascale, E.;
2019-01-01
Abstract
We discuss a systematic effect associated with measuring polarization with a continuously rotating half-wave plate (HWP). The effect was identified with the data from the E and B Experiment, which was a balloon-borne instrument designed to measure the polarization of the cosmic microwave background (CMB) as well as that from Galactic dust. The data show polarization fractions larger than 10%, while less than 3% were expected from instrumental polarization. We give evidence that the excess polarization is due to detector nonlinearity in the presence of a continuously rotating HWP. The nonlinearity couples intensity signals to polarization. We develop a map-based method to remove the excess polarization. Applying this method to the 150 (250) GHz band data, we find that 81% (92%) of the excess polarization was removed. Characterization and mitigation of this effect are important for future experiments aiming to measure the CMB B-modes with a continuously rotating HWP.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
