arXiv subjects

Maxim Markevitch

Publications and source records attributed to Maxim Markevitch.

111 records · Page 7Linked to original sources

arXiv1996

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

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.

astro-ph↗

arXiv1996

Temperature Structure of Four Hot Clusters with ASCA

ASCA data are used to obtain two-dimensional gas temperature maps of A2256, A2319, A2163 and A665. In all four, the temperature decreases significantly at off-center distances of ~1 h^{-1} Mpc. Central regions of the two nearer clusters A2256 and A2319 appear largely isothermal except for the cooler spots coincident with the subunits in their X-ray surface brightness. Although the existence of this substructure may suggest ongoing merger activity, no asymmetric features in the temperature distribution resembling those in the hydrodynamic merger simulations are apparent. In the outer parts of the clusters, the temperature declines symmetrically with radius. In A2256 and A2319, it follows a polytropic slope with gamma~1.3-1.5. This is somewhat steeper than the simulations predict for a flat CDM universe and is closer to the open universe predictions (Evrard etal 1996). The temperature drop is more prominent in the outer regions of A2163 and A665 and appears even steeper than adiabatic (although not inconsistent with it). If the gas in the outskirts of these two clusters is indeed as cool as we measure, the cluster atmospheres should be convectively unstable and transient. Also, such a steep temperature profile could not possibly emerge if the gas was heated only via the release of its own gravitational energy during infall. This may indicate the presence of an additional heat source in the inner cluster, such as merger shocks transferring energy from the dark matter to the gas.

astro-ph↗

arXiv1996

Abell 754: A Non-Head On Collision of Subclusters

We have analyzed spatially resolved spectra of A754 obtained with ASCA. The combination of spectral and imaging capabilities of ASCA has set unprecedented constraints on the hydrodynamical effects of a cluster merger. We find significant gas temperature variations over the cluster face, indicating shock heating of the atmosphere during the merger. The hottest region, >12 keV, is located in the region of the Northwest galaxy clump though the entire region along the cluster axis appears to be hotter than the mean cluster temperature (~9 keV). The cool, ~5 keV gas originally found with the HEAO1-A2 experiment, resides in the exterior of the cluster atmosphere and in plume of gas we identify with a stripped cool atmosphere of the infalling subcluster. We have also attempted to reconstruct an iron abundance map of this merging system. Though poorly constrained, no significant deviations of abundance from the mean value are apparent in the individual regions. A754 is the only cluster so far which shows the significant temperature pattern expected in a subcluster merger, in both the ROSAT (Henry & Briel 1995) and ASCA data, providing the first possibility to compare it with theoretical predictions. The observed temperature and surface brightness maps suggest that the two colliding subunits have missed each other by about 1 Mpc, and are now moving perpendicular to the cluster axis in the image plane (as, e.g., in the simulations by Evrard etal 1996).

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