X-ray XMM-Newton EPIC combined folded spectra of BB1 (filled red circles) and BB8 (filled blue squares) overplotted with their respective best-fit models (absorbed power-law) in dashed red for BB1 and dot-dashed blue for BB8. The residuals after the model subtraction are plotted in the bottom panel. The plotted data are binned to 20 counts per bin using the setplotrebin tool in XSPEC for plotting purposes only (the fitting was done with data only binned to have at least one count per bin).