Polarization posterior distributions for the two time bins of GRB 170101A with the 1σ and 2σ credibility intervals as well as that corresponding to 99% credibility. On the left, the posteriors for the first time bin range from T = 0.0 s to T = 0.5 s, while on the right for the second time bin these range from T = 0.5 s to T = 2.0 s. The polarization angle shown here is in the POLAR coordinate system; a rotation in the positive direction of 56 degrees transforms this to the coordinate system as defined by the IAU.