spectrum of Obs. 3814, relative to the continuum fit from Fig. 2. Three sets of lines are shown: H and He-like absorption lines identified by Hanke et al. (2009, black), S and Si lines from Hirsch et al. (2019, blue), transitions from the selection described in Sect. 3.4 (grey), which includes iron. Spikes with a significance of σ > 2σ are highlighted in shades of orange according to the value of σ. Lines marked in black and grey are labelled only if they are close (<0.05 Å) to a significant spike. For subsequent iron transitions belonging to the same ion, the label is shown only once. A list of spikes and associated transitions can be found in Table 1.