Context.To analyze diffuse emission that fills the field of view, one must accurately characterize the instrumental backgrounds. For the XMM-Newton EPIC-MOS instrument these backgrounds include a ...temporally variable “quiescent” component, as well as the strongly variable soft proton contamination. Aims.We have characterized the spectral and spatial response of the EPIC-MOS detectors to these background components and have developed tools to remove these backgrounds from observations. Methods.The “quiescent” component was characterized using a combination of the filter-wheel-closed data and a database of unexposed-region data. The soft proton contamination was characterized by differencing images and spectra taken during flared and flare-free intervals. Results.After application of our modeled backgrounds, the differences between independent observations of the same region of blank sky are consistent with the statistical uncertainties except when there is clear spectral evidence of solar wind charge exchange emission. Using a large sample of blank sky data, we show that strong magnetospheric SWCX emission requires elevated solar wind fluxes; observations through the densest part of the magnetosheath are not necessarily strongly contaminated with SWCX emission.
THE STRUCTURE OF THE LOCAL HOT BUBBLE Liu, W.; Chiao, M.; Collier, M. R. ...
The Astrophysical journal,
01/2017, Letnik:
834, Številka:
1
Journal Article
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ABSTRACT Diffuse X-rays from the Local Galaxy (DXL) is a sounding rocket mission designed to quantify and characterize the contribution of Solar Wind Charge eXchange (SWCX) to the Diffuse X-ray ...Background and study the properties of the Local Hot Bubble (LHB). Based on the results from the DXL mission, we quantified and removed the contribution of SWCX to the diffuse X-ray background measured by the ROSAT All Sky Survey. The "cleaned" maps were used to investigate the physical properties of the LHB. Assuming thermal ionization equilibrium, we measured a highly uniform temperature distributed around kT = 0.097 keV 0.013 keV (FWHM) 0.006 keV (systematic). We also generated a thermal emission measure map and used it to characterize the three-dimensional (3D) structure of the LHB, which we found to be in good agreement with the structure of the local cavity measured from dust and gas.
Aims. We present our analysis of a local (z = 0.04−0.2) sample of 31 galaxy clusters with the aim of measuring the density of the X-ray emitting gas in cluster outskirts. We compare our results with ...numerical simulations to set constraints on the azimuthal symmetry and gas clumping in the outer regions of galaxy clusters. Methods. We have exploited the large field-of-view and low instrumental background of ROSAT/PSPC to trace the density of the intracluster gas out to the virial radius. We stacked the density profiles to detect a signal beyond r200 and measured the typical density and scatter in cluster outskirts. We also computed the azimuthal scatter of the profiles with respect to the mean value to look for deviations from spherical symmetry. Finally, we compared our average density and scatter profiles with the results of numerical simulations. Results. As opposed to some recent Suzaku results, and confirming previous evidence from ROSAT and Chandra, we observe a steepening of the density profiles beyond ~r500. Comparing our density profiles with simulations, we find that bibradiative runs predict density profiles that are too steep, whereas runs including additional physics and/or treating gas clumping agree better with the observed gas distribution. We report high-confidence detection of a systematic difference between cool-core and non cool-core clusters beyond ~0.3r200, which we explain by a different distribution of the gas in the two classes. Beyond ~r500, galaxy clusters deviate significantly from spherical symmetry, with only small differences between relaxed and disturbed systems. We find good agreement between the observed and predicted scatter profiles, but only when the 1% densest clumps are filtered out in the ENZO simulations. Conclusions. Comparing our results with numerical simulations, we find that bibradiative simulations fail to reproduce the gas distribution, even well outside cluster cores. Although their general behavior agrees more closely with the observations, simulations including cooling and star formation convert a large amount of gas into stars, which results in a low gas fraction with respect to the observations. Consequently, a detailed treatment of gas cooling, star formation, AGN feedback, and consideration of gas clumping is required to construct realistic models of the outer regions of clusters.
We present an XMM-Newton spectrum of diffuse X-ray emission from within the solar system. The spectrum is dominated by probable C VI lines at 0.37 and 0.46 keV, an O VII line at 0.56 keV, O VIII ...lines at 0.65 and approx0.8 keV, Ne IX lines at approx0.92 keV, and Mg XI lines at approx1.35 keV. This spectrum is consistent with that expected from charge exchange emission between the highly ionized solar wind and either interstellar neutrals in the heliosphere or material from Earth's exosphere. The emission is clearly seen as a low-energy (E < 1.5 keV) spectral enhancement in one of a series of four observations of the Hubble Deep Field-North. The X-ray enhancement is concurrent with an enhancement in the solar wind measured by Advanced Composition Explorer, Wind, and Solar and Heliospheric Observatory spacecraft. The solar wind enhancement reaches a flux level an order of magnitude more intense than typical fluxes at 1 AU and has a significantly enhanced O+7/O+6 ratio. Besides being of interest in its own right for studies of the solar system, this emission can have significant consequences for observations of cosmological objects. It can provide emission lines at zero redshift, which are of particular interest in studies of diffuse thermal emission (e.g. O VII and O VIII), and which can therefore act as contamination in the spectra of objects that cover the entire detector field of view. We propose the use of solar wind monitoring data as a diagnostic to screen for such possibilities.
The solar neighbourhood is the closest and most easily studied sample of the Galactic interstellar medium, an understanding of which is essential for models of star formation and galaxy evolution. ...Observations of an unexpectedly intense diffuse flux of easily absorbed 1/4-kiloelectronvolt X-rays, coupled with the discovery that interstellar space within about a hundred parsecs of the Sun is almost completely devoid of cool absorbing gas, led to a picture of a 'local cavity' filled with X-ray-emitting hot gas, dubbed the local hot bubble. This model was recently challenged by suggestions that the emission could instead be readily produced within the Solar System by heavy solar-wind ions exchanging electrons with neutral H and He in interplanetary space, potentially removing the major piece of evidence for the local existence of million-degree gas within the Galactic disk. Here we report observations showing that the total solar-wind charge-exchange contribution is approximately 40 per cent of the 1/4-keV flux in the Galactic plane. The fact that the measured flux is not dominated by charge exchange supports the notion of a million-degree hot bubble extending about a hundred parsecs from the Sun.
Aims.We present a uniform catalog of the images and radial profiles of the temperature, abundance, and brightness for 70 clusters of galaxies observed by XMM-Newton. Methods.We use a new “first ...principles” approach to the modeling and removal of the background components; the quiescent particle background, the cosmic diffuse emission, the soft proton contamination, and the solar wind charge exchange emission. Each of the background components demonstrate significant spectral variability, several have spatial distributions that are not described by the photon vignetting function, and all except for the cosmic diffuse emission are temporally variable. Because these backgrounds strongly affect the analysis of low surface brightness objects, we provide a detailed description our methods of identification, characterization, and removal. Results.We have applied these methods to a large collection of XMM-Newton observations of clusters of galaxies and present the resulting catalog. We find significant systematic differences between the Chandra and XMM-Newton temperatures.
Three-dimensional (3D) interstellar medium (ISM) maps can be used to locate not only interstellar (IS) clouds, but also IS bubbles between the clouds that are blown by stellar winds and supernovae, ...and that are filled by hot gas. To demonstrate this and to derive a clearer picture of the local ISM, we compare our recent 3D maps of the IS dust distribution to the ROSAT diffuse X-ray background maps after removing heliospheric emission. Assuming a constant dust-to-gas ratio and homogeneous 106 K hot gas filling the cavities, we modeled the 0.25 keV surface brightness in a simple way along the Galactic plane as seen from the Sun, taking the absorption by the mapped clouds into account. Those examples illustrate the potential use of more detailed 3D distributions of the nearby ISM for interpreting the diffuse soft X-ray background.
Because M101 is nearly face-on, it provides an excellent laboratory in which to study the distribution of X-ray-emitting gas in a typical late-type spiral galaxy. We obtained a Chandra observation ...with a cumulative exposure of roughly 1 Ms to study the diffuse X-ray emission in M101. The bulk of the X-ray emission is correlated with the star formation traced by the far-UV (FUV) emission. The global FUV/X-ray correlation is nonlinear (the X-ray surface brightness is roughly proportional to the square root of the FUV surface brightness) and the small-scale correlation is poor, probably due to the delay between the FUV emission and the X-ray production in star-forming regions. The X-ray emission contains only minor contributions from unresolved stars ({approx}<3%), unresolved X-ray point sources ({approx}<4%), and individual supernova remnants ({approx}3%). The global spectrum of the diffuse emission can be reasonably well fitted with a three-component thermal model, but the fitted temperatures are not unique; many distributions of emission measure can produce the same temperatures when observed with the current CCD energy resolution. The spectrum of the diffuse emission depends on the environment; regions with higher X-ray surface brightnesses have relatively stronger hard components, but there is no significant evidence that the temperatures of the emitting components increase with surface brightness.
Investigating the Structure of Vela X Slane, P.; Lovchinsky, I.; Kolb, C. ...
The Astrophysical journal,
10/2018, Letnik:
865, Številka:
2
Journal Article
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Vela X is a prototypical example of a pulsar wind nebula whose morphology and detailed structure have been affected by interaction with the reverse shock of its host supernova remnant. The resulting ...complex of filamentary structure and mixed-in ejecta embedded in a nebula that is offset from the pulsar provides the best example we have of this middle-age state that characterizes a significant fraction of composite supernova remnants (SNRs), and perhaps all of the large-diameter pulsar wind nebulae (PWNe) seen as TeV sources. Here, we report on an XMM-Newton (hereafter XMM) Large Project study of Vela X, supplemented by additional Chandra observations. Through broad spectral modeling, as well as detailed spectral investigations of discrete emission regions, we confirm previous studies that report evidence for ejecta material within Vela X, and show that equivalent-width variations of O vii and O viii are consistent with temperature maps within the PWN that show low-temperature regions where the projected SNR emission appears to dominate emission from the ejecta. We identify spectral variations in the nonthermal emission, with hard emission being concentrated near the pulsar. We carry out investigations of the Vela X "cocoon" structure, and with hydrodynamical simulations, show that its overall properties are consistent with structures formed in the late-phase evolution of a composite SNR expanding into a surrounding medium with a density gradient, with ejecta material being swept beyond the pulsar and compressed into an elongated structure in the direction opposite the high external density.
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