Revisiting the soft X-ray excess emission in clusters of galaxies   observed with XMM-Newton
  We analyze four XMM-Newton galaxy clusters in order to test whether their soft X-ray excess emission in the 0.2-0.5 keV band as reported by Kaastra et al. (2003) maintains after the application of the current knowledge of the XMM-Newton background and calibration. We show that in the bright central 500 kpc regions the details of the background modeling are insignificant. Thus, the cluster soft excess is not a background artifact, contrary to recent claims by Bregman et al. (2006). We find evidence that the change in PN calibration between years 2002 and 2005 results in significant decrease of the soft excess signal. However, the MOS instruments measure significant amounts of soft excess, or sub-Galactic NH. These differences are compatible with the current level of uncertainty in the calibration of both instruments. 
J. Nevalainen, M. Bonamente, J. Kaastra