Lines of HONO observed towards the protostar IRAS 16293 B (in black). The first 12 lines are the identified lines of HONO in the ALMA-PILS band 7 survey. On the last row, the first 3 lines correspond to the undetected transitions that are used to constrain the best-fit model and the last two lines are those identified in other ALMA data (see Sect. 3 for more details). The 3σ limit is indicated by a dotted line. The best-fit model with T_ex = 100 K is shown in blue, while the model in red corresponds to a higher T_ex of 300 K. The spectrum at 93 GHz is extracted at the continuum peak position, given the lower spatial resolution of the data. The column density was multiplied by a factor 2 to take this difference into account (Jørgensen et al. 2016). The upper energy level is indicated in green in the bottom left corner of each panel.