Comparison of ASCA and ROSAT Cluster Temperatures: A2256, A3558 and AWM7

Abstract

We address the consistency between ASCA and ROSAT spatially-resolved cluster temperature measurements, which is of significant interest given the recent ASCA reports of temperature gradients in several hot clusters. We reanalyze ROSAT PSPC data on A2256 (originally analyzed by Briel & Henry) using the newer calibration and a technique less sensitive to the calibration uncertainties, and find a temperature decline with radius in good agreement with ASCA's. We also present ASCA temperature maps and radial profiles of A3558 and AWM7 and compare them to the published ROSAT results. In A3558, we detect an asymmetric temperature pattern and a slight radial decline. We do not find any significant temperature variations in AWM7, except around the cD galaxy. Radial temperature profiles of these two clusters are in a qualitative agreement with ROSAT. However, while their ASCA average temperatures agree with other high-energy instruments, ROSAT temperatures are lower by factors of 1.7 and 1.25, respectively. We find that including realistic estimates of the current ROSAT systematic uncertainties enlarges the temperature confidence intervals so that ROSAT measurements are consistent with others for these clusters as well. Due to the limited energy coverage of ROSAT PSPC, its results for the hotter clusters are highly sensitive to calibration uncertainties. We conclude that at the present calibration accuracy, there is no disagreement between ASCA and other instruments. On the scientific side, a ROSAT temperature underestimate for A3558 may be responsible for the anomalously high gas to total mass fraction found by Bardelli et al in this system.