Emission region projected onto the ﹩( \xi ,\Phi ) ﹩‐plane for the magnetic surface ﹩a_{f}=1﹩. Here, the emission direction is tangent to the direction of the local magnetic field. The inclination angle is ﹩\alpha =50^{\circ }﹩, the emission region extends from ﹩r_{\mathrm{in}\,}=0.67﹩ to ﹩r=R_{\mathrm{lc}\,}﹩, and the width of the polar cap angle is about 250°. The circles show the shape of the polar cap. The viewing angle ﹩\xi =100^{\circ }﹩ (horizontal dashed line) is used in the calculations for Figs. 5–9.