Spectral profiles emergent from a burst. The solid black, blue, and red curves represent Si IV 1394 Å spectral profiles as a function of Doppler velocity, recorded by IRIS at the site of an EUV burst observed with SDO/AIA. Here 0 km s⁻¹ corresponds to the rest wavelength of 1393.755 Å. The associated maps of the EUV burst are displayed in the inset. The left tile in the inset is the same as in Fig. 8a. The right tile in the inset is the Si IV 1394 Å raster map in inverted colors (integrated over ±200 km s⁻¹), covering the EUV burst. The white, blue, and red symbols mark the position of the spatial pixels we used to extract the black, blue, and red spectral profiles, respectively. For comparison, the dashed black curve is the Si IV 1394 Å spectral profile emergent from an active region UV-burst (labeled 1) discussed in Peter et al. (2014). The profile is scaled by a factor of 0.02. The strong dip in the dashed Si IV profile around − 100 km s⁻¹ is the Ni II absorption profile. See Sect. 4 for details.