Spectrum of eRO-QPE4 in quiescence (dark gray) and at the peak of the second burst in the observation eRO4-XMM (light green, following the color-coding of Fig. A.9). The dark-red line and contour represent the background spectrum and its uncertainties. Source plus background data points are shown to put the source-only models (lines and contours with the same colors) into context. Darker model contours are 1σ percentiles, lighter ones are 3σ. Individual model components are labeled.