Burst envelopes (upper panels) and PA (lower panels) for various colatitudes (vertically) and longitudes (horizontally) centred on the magnetic axis in the vicinity of the last open field lines (magnetic colatitude α ∼ α_o) at altitude r = 100R_* and for magnetic inclination i = 45°. Characteristic burst frequencies f_c (Eq. (40)) are shown as dashed purple lines, while blue contours show f_± (see Eq. (39)). Frequencies (y axis of upper plots) are represented in units of f₀ = F/r^β. Characteristic PA, Ψ_c, are dotted black lines, Ψ₊ are solid black lines and Ψ₋ dash-dotted lines (see Eq. (57)). PA are in degrees. The following fiducial values are assumed: P = 3245 ms, Ω = α_o/5 ≃ 0.09 rad, β = 3.