Panel a: polarization posterior distributions for GRB 170210A with the 1 and 2σ credibility intervals as well as that corresponding to 99% credibility. The posterior distribution clearly indicates the lack of sensitivity for this GRB for a polarization angle of 135°. The polarization angle shown here is in the POLAR coordinate system; a rotation in the positive direction of 55 degrees transforms this to the coordinate system as defined by the IAU. Panel b: measured scattering angle distribution (gray data points with a 6 degree bin size) superimposed by samples from the posterior model predictions (blue) is shown. The errors on the data points are the Poisson errors corrected for the background.