Same as Fig. 3, but for N IV 7122.98 Å. This line is absent prior to ∼1 d and after ∼5 d, because of the unsuitable ionization state of the unshocked CSM at those epochs. This spectral region contains other N IV lines at 7109.35, 7111.28, and 7127.25 Å. Here, the solid vertical bars on each side of the origin correspond to the velocity at the location in the unshocked CSM where the electron-scattering optical depth is 0.1.