1. XMM v Chandra - Cluster Analysis
Steve Snowden
NASA/Goddard Space Flight Center
EPIC Operations and Calibration Meeting
Mallorca 6-7 October 2007

2. Initial Signs
Fitted temperature radial profiles for the cluster of galaxies Abell 1795
Abell 1795 is the poster child for the discrepancy.
Chandra data (boxes) and XMM data (other)

3. Consistent Discrepancy
Comparison of multiple galaxy clusters shows a significant and systematic discrepancy between Chandra and XMM-Newton MOS results.
The higher the temperature, the greater the Chandra temperature is relative to XMM

4. Not a Question of XMM Consistency
Comparison of fitted profiles from repeated XMM observations shows excellent consistency

5. Not an Issue with Recent Changes
Comparison of fitted temperatures before and after the recent MOS QE changes.
Changes by Steve Sembay in the MOS QE does not change the situation.

6. Will Significantly Affect Science
Fundamental science in the radial profiles of clusters

7. Bottom Line – With all current corrections there is a systematic discrepancy between Chandra and XMM-Newton EPIC MOS fitted temperatures for higher temperature clusters.
The higher the fitted temperature the more likely the case that Chandra will find a higher temperature.
The difference is significant, as much as 2 keV.
This is very unlikely to be due to the larger XMM PSF.
–> cross-talk arfgen modification by Richard Saxton
–> not affected by using Chandra image for
arfgen cross-talk
–> most noticeable in flat part of profile