VLT near-infrared spectra of hard serendipitous Chandra sources

We present near-infrared long-slit spectra of eight optically-dim X-ray sources obtained with ISAAC on the Very Large Telescope. Six of the sources have hard X-ray emission with a significant fraction of the counts emerging above 2 keV. All were discovered serendipitously in the fields of three nearby galaxy clusters observed with Chandra, and identified through near-infrared imaging. The X-ray fluxes lie close to the break in the source counts. Two of the sources show narrow emission lines, and a third has a broad line. One of the narrow line-emitting sources has a clear redshift identification at z=2.18, while the other has a tentative determination based on the highest redshift detection of He I 10830 at z=1.26. The remainder have featureless spectra to deep limiting equivalent widths of 20--60 angstroms and line flux approx= 5 x 10^{-17} erg/s/cm^2 in the K-band. High-quality J, H and Ks--band images of the sources were combined with archival optical detections or limits to estimate a photometric redshift for six. Two sources show complex double morphology. The hard sources have spectral count ratios consistent with heavily obscured AGN, while the host galaxy emits much of the optical and near-infrared flux. The most likely explanation for the featureless continua is that the line photons are being scattered or destroyed by optically-thick gas and associated dust with large covering fractions.Comment: Replaced in response to problems with the PDF version of Fig 4 at arxiv.org, but not at the mirror sites (lanl.gov, soton.ac.uk). No content change

Universal trapping scaling on the unstable manifold for a collisionless electrostatic mode

An amplitude equation for an unstable mode in a collisionless plasma is derived from the dynamics on the two-dimensional unstable manifold of the equilibrium. The mode amplitude $\rho(t)$ decouples from the phase due to the spatial homogeneity of the equilibrium, and the resulting one-dimensional dynamics is analyzed using an expansion in $\rho$. As the linear growth rate $\gamma$ vanishes, the expansion coefficients diverge; a rescaling $\rho(t)\equiv\gamma^2\,r(\gamma t)$ of the mode amplitude absorbs these singularities and reveals that the mode electric field exhibits trapping scaling $|E_1|\sim\gamma^2$ as $\gamma\rightarrow0$. The dynamics for $r(\tau)$ depends only on the phase $e^{i\xi}$ where $d\epsilon_{{k}} /dz=|{\epsilon_{{k}}}|e^{-i\xi/2}$ is the derivative of the dielectric as $\gamma\rightarrow0$.Comment: 11 pages (Latex/RevTex), 2 figures available in hard copy from the Author ([email protected]); paper accepted by Physical Review Letter

The 3D structure of the Lagrangian acceleration in turbulent flows

We report experimental results on the three dimensional Lagrangian acceleration in highly turbulent flows. Tracer particles are tracked optically using four silicon strip detectors from high energy physics that provide high temporal and spatial resolution. The components of the acceleration are shown to be statistically dependent. The probability density function (PDF) of the acceleration magnitude is comparable to a log-normal distribution. Assuming isotropy, a log-normal distribution of the magnitude can account for the observed dependency of the components. The time dynamics of the acceleration components is found to be typical of the dissipation scales whereas the magnitude evolves over longer times, possibly close to the integral time scale.Comment: accepted for publication in Physical Review Letter

Extended X-Ray Emission from QSOs

We report Chandra ACIS observations of the fields of 4 QSOs showing strong extended optical emission-line regions. Two of these show no evidence for significant extended X-ray emission. The remaining two fields, those of 3C 249.1 and 4C 37.43, show discrete (but resolved) X-ray sources at distances ranging from ~10 to ~40 kpc from the nucleus. In addition, 4C 37.43 also may show a region of diffuse X-ray emission extending out to ~65 kpc and centered on the QSO. It has been suggested that extended emission-line regions such as these may originate in the cooling of a hot intragroup medium. We do not detect a general extended medium in any of our fields, and the upper limits we can place on its presence indicate cooling times of at least a few 10^9 years. The discrete X-ray emission sources we detect cannot be explained as the X-ray jets frequently seen associated with radio-loud quasars, nor can they be due to electron scattering of nuclear emission. The most plausible explanation is that they result from high-speed shocks from galactic superwinds resulting either from a starburst in the QSO host galaxy or from the activation of the QSO itself. Evidence from densities and velocities found from studies of the extended optical emission around QSOs also supports this interpretation.Comment: Accepted by ApJ. 9 pages including 5 figure

The optical variability of the narrow line Seyfert 1 galaxy IRAS 13224-3809

We report on a short optical monitoring programme of the narrow-line Seyfert 1 Galaxy IRAS 13224-3809. Previous X-ray observations of this object have shown persistent giant variability. The degree of variability at other wavelengths may then be used to constrain the conditions and emission processes within the nucleus. Optical variability is expected if the electron population responsible for the soft X-ray emission is changing rapidly and Compton-upscattering infrared photons in the nucleus, or if the mechanism responsible for X-ray emission causes all the emission processes to vary together. We find that there is no significant optical variability with a firm upper limit of 2 per cent and conclude that the primary soft X-ray emission region produces little of the observed optical emission. The X-ray and optical emission regions must be physically distinct and any reprocessing of X-rays into the optical waveband occurs some distance from the nucleus. The lack of optical variability indicates that the energy density of infrared radiation in the nucleus is at most equal to that of the ultraviolet radiation since little is upscattered into the optical waveband. The extremely large X-ray variability of IRAS 13224-3809 may be explained by relativistic boosting of more modest variations. Although such boosting enhances X-ray variability over optical variability, this only partially explains the lack of optical variability.Comment: 5 pages with 8 postscript figures. Accepted for publication in MNRA

Exploring Vulnerability and Interdependency of UK Infrastructure Using Key-Linkages Analysis

It has been argued the UK has experienced significant underinvestment in critical infrastructure over the last two decades. This in turn has resulted in infrastructure that is less capable of assisting the UK economy to grow. This article seeks to augment the relevant evidence by under-taking an in-depth analysis of the inter-linkages and economic contributions from infrastructure within the UK. It explores the relationship between nine infrastructure sectors and how these sectors contribute to the rest of the UK economy using key-linkage analysis. Each infrastructure sector is shown to be unique in the way it interacts with other economic sectors and in the form of contribution it makes to the economy overall. Infrastructure is a necessary and important part of economic development. The analysis finds that over the last 23 years there has been a decline in the relative economic contribution from infrastructure to UK GVA. Only two infrastructure sectors increased their relative contribution to GVA since 1992. These were the water transport sector and sewerage and sanitary services sector. Railway transport and gas distribution have had the largest relative decline in contribution towards UK GVA with relative contributions decreasing by over 50% since 1992. The three most important infrastructure sectors contributing to UK GDP are land transport, electricity production and distribution and telecommunications respectively.Funding for this research was provided by the Engineering and Physical Sciences Research Council (EPSRC) grant number EP/101344X/1 through the Infrastructure Transitions Research Consortium (ITRC).This is the final version of the article. It first appeared from Springer via http://dx.doi.org/10.1007/s11067-015-9302-

Relativistic semiclassical approach in strong-field nonlinear photoionization

Nonlinear relativistic ionization phenomena induced by a strong laser radiation with elliptically polarization are considered. The starting point is the classical relativistic action for a free electron moving in the electromagnetic field created by a strong laser beam. The application of the relativistic action to the classical barrier-suppression ionization is briefly discussed. Further the relativistic version of the Landau-Dykhne formula is employed to consider the semiclassical sub-barrier ionization. Simple analytical expressions have been found for: (i) the rates of the strong-field nonlinear ionization including relativistic initial and final state effects; (ii) the most probable value of the components of the photoelectron final state momentum; (iii) the most probable direction of photoelectron emission and (iv) the distribution of the photoelectron momentum near its maximum value.Comment: 13 pages, 3 figures, to be published in Phys. Rev.

Mentalising and social problem solving in adults with Asperger's syndrome

It is well established that autistic spectrum disorder is linked to difficulties with mentalising, but the ways in which this affects everyday behaviour is less well understood. This study explored the nature and extent of difficulties in everyday social functioning in adults with Asperger's syndrome (AS), since increased understanding can enhance the development of more effective intervention strategies. Methods Individuals with AS (n=21) were compared with healthy control participants (n=21) on three tests of social cognition: the Mentalistic Interpretation task, which assesses interpretation of sarcasm and actions; the Social Problem Fluency task, which assesses ability to generate problem solutions; and the Social Problem Resolution task, which assesses judgement in selecting problem solutions. Results Comprehension of both sarcastic remarks and actions was impaired in those with AS on the mentalistic interpretation task. Participants with AS showed difficulties in identifying the awkward elements of everyday social scenarios, and they were also impaired in generating problem solutions but not in judging alternative solutions on the social problem fluency and resolution tasks. Conclusions These tasks potentially provide a means of profiling strengths and weaknesses in social processing, which in turn has implications for informing clinical evaluation and training. © 2013 Taylor & Francis

The Properties of Poor Groups of Galaxies: II. X-ray and Optical Comparisons

We use ROSAT PSPC data to study the X-ray properties of a sample of twelve poor groups that have extensive membership information (Zabludoff and Mulchaey 1997; Paper I). Diffuse X-ray emission is detected in nine of these groups. In all but one of the X-ray detected groups, the X-ray emission is centered on a luminous elliptical galaxy. Fits to the surface brightness profiles of the X-ray emission suggest the presence of two X-ray components in these groups. The first component is centered on the central elliptical galaxy. The location and extent of this component, combined with its X-ray temperature and luminosity, favor an origin in the interstellar medium of the central galaxy. Alternatively, the central component may be the result of a large-scale cooling flow. The second X-ray component is detected out to a radius of at least 100-300 kpc. This component follows the same relationships found among the X-ray temperature, X-ray luminosity and optical velocity dispersion of rich clusters. This result suggests that the X-ray detected groups are low-mass versions of clusters and that the extended gas component can properly be called the intragroup medium, in analogy to the intracluster medium in clusters. We also find a trend for the position angle of the optical light in the central elliptical galaxy to align with the position angle of the large-scale X-ray emission. (Abridged)Comment: 38 pages, AASLaTeX with 16 PS figures. Figure 1a-1l available in gzipped postscript format at ftp://corvus.ociw.edu/pub/mulchae