Histogram of brightness temperature values in the ¹²CO maps in the 80−81 km s^-1 velocity range (solid line, Zhou et al. 2009, also visible in the lower panel of Fig. 1) which shows the molecular cloud interacting with the remnant. On this, we superimpose the histogram of the same temperatures at the location of the 18 hard X-ray sources detected in the XMM-Newton observation (dashed line). The r value is the Pearson correlation coefficient, which indicates that there is a positive correlation (see Appendix A for details). The source peak is offset toward higher values than the cloud mean value, indicating that X-ray sources cluster at brighter-than-average CO map points.