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Register a new userThe late merging phase of a galaxy cluster : XMM EPIC Observations of A3266
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We present a mosaic of five XMM-Newton observations of the nearby ($z=0.0594$) merging galaxy cluster Abell 3266. We use the spectro-imaging capabilities of xmm to build precise (projected) temperature, entropy, pressure and Fe abundance maps. The temperature map exhibits a curved, large-scale hot region, associated with elevated entropy levels, very similar to that foreseen in numerical simulations. The pressure distribution is disturbed in the central region but is remarkably regular on large scales. The Fe abundance map indicates that metals are inhomogeneously distributed across the cluster. Using simple physical calculations and comparison with numerical simulations, we discuss in detail merging scenarios that can reconcile the observed gas density, temperature and entropy structure, and the galaxy density distribution.
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Analysis of a 30,000 s X-ray observation of the Abell 3266 galaxy cluster with the ACIS on board the Chandra Observatory has produced several new insights into the cluster merger. The intracluster medium has a non-monotonically decreasing radial abundance profile. We argue that the most plausible origin for the abundance enhancement is unmixed, high abundance subcluster gas from the merger. The enrichment consists of two stages: off-center deposition of a higher abundance material during a subcluster merger followed by a strong, localized intracluster wind that acts to drive out the light elements, producing the observed abundance enhancement. The wind is needed to account for both an increase in the heavy element abundance and the lack of an enhancement in the gas density. Dynamical evidence for the wind includes: (1) a large scale, low surface brightness feature perpendicular to the merger axis that appears to be an asymmetric pattern of gas flow to the northwest, away from the center of the main cluster, (2) compressed gas in the opposite direction (toward the cluster center), and (3), the hottest regions visible in the temperature map coincide with the proposed merger geometry and the resultant gas flow. The Chandra data for the central region of the main cluster shows a slightly cooler, filamentary region that is centered on the central cD galaxy and is aligned with the merger axis directly linking the dynamical state of the cD to the merger. Overall, the high spectral/spatial resolution Chandra observations support our earlier hypothesis (Henriksen, Donnelly, & Davis 1999) that we are viewing a minor merger in the plane of the sky.
We studied the intracluster medium of the galaxy cluster CIZA J2242.8+5301 using deep XMM-Newton observations. The cluster hosts a remarkable 2-Mpc long, ~50-kpc wide radio relic that has been nicknamed the Sausage. A smaller, more irregular counter-relic is also present, along with a faint giant radio halo. We analysed the distribution of the ICM physical properties, and searched for shocks by trying to identify density and temperature discontinuities. East of the southern relic, we find evidence of shock compression corresponding to a Mach number of 1.3, and speculate that the shock extends beyond the length of the radio structure. The ICM temperature increases at the northern relic. More puzzling, we find a wall of hot gas east of the cluster centre. A partial elliptical ring of hot plasma appears to be present around the merger. While radio observations and numerical simulations predict a simple merger geometry, the X-ray results point towards a more complex merger scenario.
An XMM-Newton imaging spectroscopy analysis of the galaxy cluster A1644 is presented. A1644 is a complex merging system consisting of a main and a sub cluster. A trail of cool, metal-rich gas has been discovered close to the sub cluster. The combination of results from X-ray, optical, and radio data, and a comparison to a hydrodynamical simulation suggest that the sub cluster has passed by the main cluster off-axis and a fraction of its gas has been stripped off during this process. Furthermore, for this merging system, simple effects are illustrated which can affect the use of clusters as cosmological probes. Specifically, double clusters may affect estimates of the cluster number density when treated as a single system. Mergers, as well as cool cores, can alter the X-ray luminosity and temperature measured for clusters, causing these values to differ from those expected in equilibrium.
We examine the possible acceleration mechanisms of the relativistic particles responsible for the extended radio emission in Abell 520. We used new LOFAR 145 MHz, archival GMRT 323 MHz and VLA 1.5 GHz data to study the morphological and spectral properties of extended cluster emission. The observational properties are discussed in the framework of particle acceleration models associated with cluster merger turbulence and shocks. In Abell 520, we confirm the presence of extended synchrotron radio emission that has been classified as a radio halo. The comparison between the radio and X-ray brightness suggests that the halo might originate in a cocoon rather than from the central X-ray bright regions of the cluster. The halo spectrum is roughly uniform on the scale of 66 kpc. There is a hint of spectral steepening from the SW edge towards the cluster centre. Assuming DSA, the radio data are suggestive of a shock of $mathcal{M}_{SW}=2.6_{-0.2}^{+0.3}$ that is consistent with the X-ray derived estimates. This is in line with the scenario in which relativistic electrons in the SW radio edge gain their energies at the shock front via acceleration of either thermal or fossil electrons. We do not detect extended radio emission ahead of the SW shock that is predicted if the emission is the result of adiabatic compression. An X-ray surface brightness discontinuity is detected towards the NE region that may be a counter shock of $mathcal{M}_{NE}^{X}=1.52pm0.05$. This is lower than the value predicted from the radio emission ($mathcal{M}_{NE}=2.1pm0.2$). Our observations indicate that the SW radio emission in Abell 520 is likely effected by the prominent X-ray detected shock in which radio emitting particles are (re-)accelerated through the Fermi-I mechanism. The NE X-ray discontinuity that is approximately collocated with an edge in the radio emission hints at the presence of a counter shock.
We present spin-resolved X-ray data of the neutron star binary Her X-1. We find evidence that the Iron line at 6.4 keV originates from the same location as the blackbody X-ray component. The line width and energy varies over both the spin period and the 35 day precession period. We also find that the correlation between the soft and hard X-ray light curves varies over the 35 day period.
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