Chandra Observation of a 300 kpc Hydrodynamic Instability in the Intergalactic Medium of the Merging Cluster of Galaxies A3667

We present results from the combination of two Chandra pointings of the central region of the cluster of galaxies A3667. From the data analysis of the first pointing Vikhlinin et al. reported the discovery of a prominent cold front which is interpreted as the boundary of a cool gas cloud moving through the hotter ambient gas. Vikhlinin et al. discussed the role of the magnetic fields in maintaining the apparent dynamical stability of the cold front over a wide sector at the forward edge of the moving cloud and suppressing transport processes across the front. In this Letter, we identify two new features in the X-ray image of A3667: i) a 300 kpc arc-like filamentary X-ray excess extending from the cold gas cloud border into the hotter ambient gas; ii) a similar arc-like filamentary X-ray depression that develops inside the gas cloud. The temperature map suggests that the temperature of the filamentary excess is consistent with that inside the gas cloud while the temperature of the depression is consistent with that of the ambient gas. We suggest that the observed features represent the first evidence for the development of a large scale hydrodynamic instability in the cluster atmosphere resulting from a major merger. This result confirms previous claims for the presence of a moving cold gas cloud into the hotter ambient gas. Moreover it shows that, although the gas mixing is suppressed at the leading edge of the subcluster due to its magnetic structure, strong turbulent mixing occurs at larger angles to the direction of motion. We show that this mixing process may favor the deposition of a nonnegligible quantity of thermal energy right in the cluster center, affecting the development of the central cooling flow.Comment: Replaced to match version accepted for publication in ApJL; some changes on text. 4 pages, 3 color figures and 2 BW figures, emulateapj

A search for x-ray counterparts of gamma-ray bursts with the ROSAT PSPC

We search for faint X-ray bursts with duration 10--300 seconds in the ROSAT PSPC pointed observations with a total exposure of 1.6e7 seconds. We do not detect any events shorter than ~100s, i.e. those that could be related to the classic gamma-ray bursts. At the same time, we detect a number of long flares with durations of several hundred seconds. Most, but not all, of the long flares are associated with stars. If even a small number of those long flares, that cannot identified with stars, are X-ray afterglows of GRB, the number of X-ray afterglows greatly exceeds the number of BATSE GRB. This would imply that the beaming factor of gamma-rays from the burst should be >100. The non-detection of any short bursts in our data constrains the GRB counts at the fluences 1--2.5 orders of magnitude below the BATSE limit. The constrained burst counts are consistent with the extrapolation of the BATSE log N - log S relation. Finally, our results do not confirm a reality of short X-ray flashes found in the Einstein IPC data by Gotthelf, Hamilton and Helfand.Comment: Accepted to ApJ Letters. 4 pages with 3 figures, LaTeX2

Lynx X-Ray Observatory: Response to the First Astro 2020 Decadal Survey Request for Information

This document serves as the Lynx Teams response to the first Request For Information (RFI) from the 2020 Decadal Survey in Astronomy and Astrophysics. Detailed answers to all of the questions asked in this RFI can be found in the Lynx Concept Study Report, Supplementary Technology Roadmaps, and the Lynx Cost Book

Effects of Galaxy Formation on Thermodynamics of the Intracluster Medium

We present detailed comparisons of the intracluster medium (ICM) in cosmological Eulerian cluster simulations with deep Chandra observations of nearby relaxed clusters. To assess the impact of galaxy formation, we compare two sets of simulations, one performed in the non-radiative regime and another with radiative cooling and several physical processes critical to various aspects of galaxy formation: star formation, metal enrichment and stellar feedback. We show that the observed ICM properties outside cluster cores are well-reproduced in the simulations that include cooling and star formation, while the non-radiative simulations predict an overall shape of the ICM profiles inconsistent with observations. In particular, we find that the ICM entropy in our runs with cooling is enhanced to the observed levels at radii as large as half of the virial radius. We also find that outside cluster cores entropy scaling with the mean ICM temperature in both simulations and Chandra observations is consistent with being self-similar within current error bars. We find that the pressure profiles of simulated clusters are also close to self-similar and exhibit little cluster-to-cluster scatter. The X-ray observable-total mass relations for our simulated sample agree with the Chandra measurements to \~10%-20% in normalization. We show that this systematic difference could be caused by the subsonic gas motions, unaccounted for in X-ray hydrostatic mass estimates. The much improved agreement of simulations and observations in the ICM profiles and scaling relations is encouraging and the existence of tight relations of X-ray observables, such as Yx, and total cluster mass and the simple redshift evolution of these relations hold promise for the use of clusters as cosmological probes.Comment: 14 pages, 6 figures. Matches version accepted to Ap

Testing X-ray Measurements of Galaxy Clusters with Cosmological Simulations

X-ray observations of galaxy clusters potentially provide powerful cosmological probes if systematics due to our incomplete knowledge of the intracluster medium (ICM) physics are understood and controlled. In this paper, we present mock Chandra analyses of cosmological cluster simulations and assess X-ray measurements of galaxy cluster properties using a model and procedure essentially identical to that used in real data analysis. We show that reconstruction of three-dimensional ICM density and temperature profiles is excellent for relaxed clusters, but still reasonably accurate for unrelaxed systems. The total ICM mass is measured quite accurately (<6%) in all clusters, while the hydrostatic estimate of the gravitationally bound mass is biased low by about 5%-20% through the virial region, primarily due to additional pressure support provided by subsonic bulk motions in the ICM, ubiquitous in our simulations even in relaxed systems. Gas fraction determinations are therefore biased high; the bias increases toward cluster outskirts and depends sensitively on its dynamical state, but we do not observe significant trends of the bias with cluster mass or redshift. We also find that different average ICM temperatures, such as the X-ray spectroscopic Tspec and gas-mass-weighted Tmg, are related to each other by a constant factor with a relatively small object-to-object scatter and no systematic trend with mass, redshift or the dynamical state of clusters. We briefly discuss direct applications of our results for different cluster-based cosmological tests.Comment: 11 pages, 6 figures, submitted to Ap

Predicting Single-Temperature Fit to Multi-Component Thermal Plasma Spectra

Observed X-ray spectra of hot gas in clusters, groups, and individual galaxies are commonly fit with a single-temperature thermal plasma model even though the beam may contain emission from components with different temperatures. Recently, Mazzotta et al. pointed out that thus derived T_spec can be significantly different from commonly used definitions of average temperature, such as emission- or emission measure-weighted T, and found an analytic expression for predicting T_spec for a mixture of plasma spectra with relatively hot temperatures (T>3 keV). In this Paper, we propose an algorithm which can accurately predict T_spec in a much wider range of temperatures (T>0.5 keV), and for essentially arbitrary abundance of heavy elements. This algorithm can be applied in the deprojection analysis of objects with the temperature and metallicity gradients, for correction of the PSF effects, for consistent comparison of numerical simulations of galaxy clusters and groups with the X-ray observations, and for estimating how emission from undetected components can bias the global X-ray spectral analysis.Comment: Submitted to ApJ. 6 emulateapj pages. Updated in response to the referee's comments. Now includes parameters for XMM PN and MOS and ASCA GIS and SI

Physics of the Merging Clusters Cygnus A, A3667, and A2065

We present ASCA gas temperature maps of the nearby merging galaxy clusters Cygnus A, A3667, and A2065. Cygnus A appears to have a particularly simple merger geometry that allows an estimate of the subcluster collision velocity from the observed temperature variations. We estimate it to be ~2000 km/s. Interestingly, this is similar to the free-fall velocity that the two Cygnus A subclusters should have achieved at the observed separation, suggesting that merger has been effective in dissipating the kinetic energy of gas halos into thermal energy, without channeling its major fraction elsewhere (e.g., into turbulence). In A3667, we may be observing a spatial lag between the shock front seen in the X-ray image and the corresponding rise of the electron temperature. A lag of the order of hundreds of kiloparsecs is possible due to the combination of thermal conduction and a finite electron-ion equilibration time. Forthcoming better spatial resolution data will allow a direct measurement of these phenomena using such lags. A2065 has gas density peaks coincident with two central galaxies. A merger with the collision velocity estimated from the temperature map should have swept away such peaks if the subcluster total mass distributions had flat cores in the centers. The fact that the peaks have survived (or quickly reemerged) suggests that the gravitational potential also is strongly peaked. Finally, the observed specific entropy variations in A3667 and Cygnus A indicate that energy injection from a single major merger may be of the order of the full thermal energy of the gas. We hope that these order of magnitude estimates will encourage further work on hydrodynamic simulations, as well as more quantitative representation of the simulation results.Comment: Corrected the Cyg-A figure (errors shown were 1-sigma not 90%); text unchanged. ApJ in press. Latex, 5 pages, 3 figures (2 color), uses emulateapj.st

The X-Ray Surveyor Mission Concept Study Plan

No abstract availabl