Evolution of Si IV 1393.76 Å line profiles inside the UV burst (same points as in Fig. A.1) for three times (each row distant of 42 s and 14 s, respectively) and for three pixels distant of one arcsec (between each column). The UV burst is located in slit 1. The red profile is the reference profile in the quiet chromosphere. The red arrows indicate the absorption by the Ni II 1393.33 Å and Fe II 1393.589 Å. The blue arrows indicate the dip in the central Si IV profile due to self-absorption.