Resonance signatures in the residual flux. (a–c) 0.08–0.12 Hz band-pass filtered PADs of (a) 11.4 keV, (b) 5.8 keV and (c) 4.3 keV proton residual fluxes in the solar wind frame between 13:46:50–13:48:50 UT, derived from STEP measurements. The horizontal dashed black lines in (a–c) refer to the PA range of 15°–75°. (d) Stacked plots of band-pass filtered residual fluxes for 3.1–15.7 keV protons averaged between 15°–75° PA. The inclined black and dashed magenta lines are used to guide the eye. (e) 0.08–0.12 Hz band-pass filtered magnetic field B_⊥, 1 and B_⊥, 2 components in the mean (30 s) field-aligned coordinates. (f) Phase difference between the residual flux and B_⊥, 2 for each energy channel presented in (d) averaged between 13:46:50–13:48:50 UT, calculated by the cross-wavelet analysis described in Grinsted et al. (2004). The colored dots correspond to the energy channels in (d). The black curve shows the least squares fit of $\varphi =arctan\frac{a}{V_{\Vert }-V_{\mathrm{R}}}+{\varphi }_0$, in which ϕ and V_∥ are the phase difference and the parallel velocity, and a, V_R, ϕ₀ are free parameters. The vertical dashed line presents the V_R derived from the fitting procedure. (g) Energy Spectra of time-averaged proton phase space density averaged over 15°–75° PA. The vertical dashed line marks the energy corresponding to V_R.