https://arxiv.org/abs/astro-ph/0203311
[astro-ph/0203311] Comparison of XMM-Newton EPIC, Chandra ACIS-S3, ASCA SIS and GIS, and ROSAT PSPC...
Abstract page for arXiv paper astro-ph/0203311: Comparison of XMM-Newton EPIC, Chandra ACIS-S3, ASCA SIS and GIS, and ROSAT PSPC Results for G21.5-0.9,...