Sinusoidal patterns of RM as a function of galactic longitude (l) in bins of 10°, are presented for three different configurations: the entire data cube is considered (left; setup A); only the volume enclosed by the outer edges of the bubble is used (center; setup B); and the bubble is carved out from the data cube (right; setup C). The profiles are obtained from averaging the latitude range 40 ° < b < 45° (red) and −45 ° < b < −40° (blue). The error bars on the points show the standard deviation of the values in each bin. The least-squares fit parameters of the first three terms of a Fourier series in l,  RM(l) = C₀ + C₁sin(l + ϕ₁) + C₂sin2(l + ϕ₂) , are reported.