With the forthcoming release of high precision polarization measurements such as from the Planck satellite it becomes critical to evaluate the performance of estimators for the polarization fraction and angle These two physical quantities suffer from a well-known bias in the presence of measurement noise as has been described in part I of this series In this paper part II of the series we explore the extent to which various estimators may correct the bias Traditional frequentist estimators of the polarization fraction are compared with two recent estimators one inspired by a Bayesian analysis and a second following an asymptotic method We investigate the sensitivity of these estimators to the asymmetry of the covariance matrix which may vary over large datasets We present for the first time a comparison among polarization angle estimators and evaluate the statistical bias on the angle that appears when the covariance matrix exhibits effective ellipticity We also address the question of the accuracy of the polarization fraction and angle uncertainty estimators The methods linked to the credible intervals and to the variance estimates are tested against the robust confidence interval method From this pool of estimators we build recipes adapted to different use-cases build a mask compute large maps and deal with low S/N data More generally we show that the traditional estimators suffer from discontinuous distributions at low S/N while the asymptotic and Bayesian methods do not Attention is given to the shape of the output distribution of the estimators and is compared with a Gaussian In this regard the new asymptotic method presents the best performance while the Bayesian output distribution is shown to be strongly asymmetric with a sharp cut at low S/NFinally we present an optimization of the estimator derived from the Bayesian analysis using adapted priors
from HAL : Dernières publications http://ift.tt/1wqEmDy
from HAL : Dernières publications http://ift.tt/1wqEmDy
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