...
"XMM-Newton and Chandra Cross Calibration Using HIFLUGCS Galaxy Clusters", Schellenberger, G., et al., 2015, A&A, 575, 30
"Reconciling Planck cluster counts and cosmology? Chandra/XMM instrumental calibration and hydrostatic mass bias", Israel, H., et al., 2015, MNRAS, 448, 814
...