Panel a: light curve of GRB 170320A as measured by POLAR, where T = 0 s is defined as the T0 reported by POLAR in the original GCN (Zhao et al. 2017). Panel b: joint spectral fit result for 170320A. The number of counts as detected by both POLAR (blue) is shown along with the best-fitting spectrum folded through the instrument response in yellow. The residuals are shown in the bottom of the figure.