Identify the specific systematic causing eROSITA–Chandra/XMM temperature discrepancies

Identify the specific calibration or analysis systematic responsible for the systematic temperature discrepancies observed between SRG/eROSITA and Chandra/ACIS and between SRG/eROSITA and XMM-Newton/EPIC across the analyzed energy bands.

Background

The study compares intracluster medium temperatures from SRG/eROSITA to those from Chandra/ACIS and XMM-Newton/EPIC, finding consistent systematic offsets that grow with cluster temperature, especially in harder bands. The authors investigate multiple possible sources—multiphase gas, metallicity–temperature degeneracy, Galactic absorption, non-Gaussian scatter, sample selection, and eROSITA TM module effects—but none accounts for the discrepancy.

Consequently, while effective area calibration uncertainties are suspected, the precise systematic(s) responsible remain unidentified. Pinpointing the cause is necessary to improve cross-calibration and enable unbiased joint analyses across X-ray observatories.

References

We could not identify a specific systematic that had a strong effect on the eROSITA cross-calibration with Chandra and XMM-Newton, and more work is needed to obtain conclusive results about some of the potential biases.

— The SRG/eROSITA All-Sky Survey: SRG/eROSITA cross-calibration with Chandra and XMM-Newton using galaxy cluster gas temperatures  (2401.17297 - Migkas et al., 2024) in Section 7 (Summary and conclusions)