Distribution of simulated off-axis bursts as compared with that of on-axis ones. a) All mock bursts on the E_p − E_iso plane. b) All mock bursts on the E_p − L_p plane. The dash-dotted line and the dotted line correspond to the best-fit result for on- and off-axis samples, respectively. The dashed lines represent the corresponding 3σ confidence level. Most of the off-axis bursts are too weak to appear in the two panels here.