— Eric Hivon 2018/07/13 03:56

Same exercise as on July 02, this time considering a beam at 150GHz located 10cm in the Y direction from the focal plane center. We see this time a much larger contamination of BB, which looks like an ell-increasing leakage from EE to BB, probably due to the m=4 components of the beam map.

First GRASP simulations by Karl Young of PICO main beam responses at 150GHz at the center of focal plane, for 2 orthogonal detectors.

The FWHMs were found to be ~4.9arcmin, the elongations (ratio of the major and minor axes) 1.01, and the ratios of U/I about 1.e-4 for both beams, meaning that the beams are very much co-polar, with very little spurious rotation (~<0.5 arcmin).

The same exercise would have to be repeated at a more representative position (ie, off-axis) where systematics (=elongation of beam and rotation of polarization) could be larger.

The plot below shows how the various spectra are affected for either the purely copolar beam (ignoring the U beam component, green dashes) or the “full” beam (red dashes), as computed by QuickPol assuming a scanning strategy adapted from July 1st 2018 baseline (α=30º, T_prec=10h, β=65º, T_spin=1mn, sampling = 151Hz, 2 years of observation, N_side=1024).

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