Modulation of the simulated photons in GBM. The colors indicate different polarization degrees. The dashed line shows the detected counts with the shaded region indicating the 1σ, 2σ, and 3σ uncertainties (statistical only). Stars indicate the best χ² value computed for all detectors by scanning the PA–PD grid (Figure 5), which is (PA, PD) = (30°,  80%). We extended the x-axis to show two periods for clarity.