Angle-resolved photoemission spectroscopy of band tails in lightly doped cuprates

We amend ab initio strongly-correlated band structures by taking into account the band-tailing phenomenon in doped charge-transfer Mott-Hubbard insulators. We show that the photoemission from band tails accounts for sharp "quasi-particle" peaks, rapid loss of their intensities in some directions of the Brillouin zone ("Fermi-arcs") and high-energy "waterfall" anomalies as a consequence of matrix-element effects of disorder-localised states in the charge-transfer gap of doped cuprates.Comment: 4 pages, 4 figure

ROSAT PSPC observations of Cygnus-A : X-ray spectra of the cooling flow and hot spots

We present a {\it ROSAT} Position Sensitive Proportional Counter (PSPC) observation of the powerful radio galaxy Cygnus-A. The X-ray emission in the {\it ROSAT} band is dominated by thermal emission from the hot intracluster medium of the associated cluster. Image deprojection confirms the existence of a significant cluster cooling flow with total mass deposition rate of $\sim 250\,{\rm M}_\odot\,{\rm yr}^{-1}$ and a (Hubble time) cooling radius of $\sim 180$\,kpc. Spectral data show the gradient in the emission-weighted mean temperature with the temperature decreasing towards the centre of the cluster. We also find signatures of the radio source: in particular, we detect the X-ray emission from the western radio hot spot previously found by the {\it ROSAT} High Resolution Imager (HRI). We find the emission from the hot spot to be hard and discuss the physical implications of this result.Comment: uuencoded compressed postscript. The preprint is also available at http://www.ast.cam.ac.uk/preprint/PrePrint.htm

Special relativistic effects on the strength of the fluorescent K-alpha iron line from black hole accretion disks

The broad iron K$\alpha$ emission line, commonly seen in the X-ray spectrum of Seyfert nuclei, is thought to originate when the inner accretion disk is illuminated by an active disk-corona. We show that relative motion between the disk and the X-ray emitting material can have an important influence on the observed equivalent width (EW) of this line via special relativistic aberration and Doppler effects. We suggest this may be relevant to understanding why the observed EW often exceeds the prediction of the standard X-ray reflection model. Several observational tests are suggested that could disentangle these special relativistic effects from iron abundance effects.Comment: 5 pages, 3 postscript figures. Accepted for publication in MNRAS (pink pages). Also available at http://rocinante.Colorado.EDU/~chris/html_papers/special/special.htm

Are the Nuclei of Seyfert 2 Galaxies Viewed Face-On?

We show from modeling the Fe Kalpha line in the ASCA spectra of four X-ray bright narrow emission line galaxies (Seyfert types 1.9 and 2) that two equally viable physical models can describe the observed line profile. The first is discussed by Turner et al. (1998) and consists of emission from a nearly pole-on accretion disk. The second, which is statistically preferred, is a superposition of emission from an accretion disk viewed at an intermediate inclination of about 48 degrees and a distinct, unresolved feature that presumably originates some distance from the galaxy nucleus. The intermediate inclination is entirely consistent with unified schemes and our findings challenge recent assertions that Seyfert 2 galaxies are preferentially viewed with their inner regions face-on. We derive mean equivalent widths for the narrow and disk lines of =60 eV and = 213 eV, respectively. The X-ray data are well described by a geometry in which our view of the active nucleus intersects and is blocked by the outer edges of the obscuring torus, and therefore do not require severe misalignments between the accretion disk and the torus.Comment: 19 pages, 3 postscript figures. Accepted for publication in ApJ

Energetic Impact of Jet Inflated Cocoons in Relaxed Galaxy Clusters

Jets from active galactic nuclei (AGN) in the cores of galaxy clusters have the potential to be a major contributor to the energy budget of the intracluster medium (ICM). To study the dependence of the interaction between the AGN jets and the ICM on the parameters of the jets themselves, we present a parameter survey of two-dimensional (axisymmetric) ideal hydrodynamic models of back-to-back jets injected into a cluster atmosphere (with varying Mach numbers and kinetic luminosities). We follow the passive evolution of the resulting structures for several times longer than the active lifetime of the jet. The simulations fall into roughly two classes, cocoon-bounded and non-cocoon bounded sources. We suggest a correspondence between these two classes and the Faranoff-Riley types. We find that the cocoon-bounded sources inject significantly more entropy into the core regions of the ICM atmosphere, even though the efficiency with which energy is thermalized is independent of the morphological class. In all cases, a large fraction (50--80%) of the energy injected by the jet ends up as gravitational potential energy due to the expansion of the atmosphere.Comment: 12 pages, Accepted for publication in Ap

An extended multi-zone model for the MCG-6-30-15 warm absorber

The variable warm absorber seen with {\em ASCA} in the X-ray spectrum of MCG$-$6-30-15 shows complex time behaviour in which the optical depth of OVIII anticorrelates with the flux whereas that of OVII is unchanging. The explanation in terms of a two zone absorber has since been challenged by {\em BeppoSAX} observations. These present a more complicated behaviour for the OVIII edge. We demonstrate here that the presence of a third, intermediate, zone can explain all the observations. In practice, warm absorbers are likely to be extended, multi-zone regions of which only part causes directly observable absorption edges at any given time.Comment: 5 pages, 6 figures, accepted for publication in MNRA

A deep Chandra observation of Abell 4059: a new face to radio-mode AGN feedback?

A deep Chandra observation of the cooling core cluster Abell 4059 (A4059) is presented. Previous studies have found two X-ray cavities in the central regions of A4059 together with a ridge of X-ray emission 20kpc south-west of the cluster center. These features are clearly related to the radio galaxy PKS2354-35 which resides in the cD galaxy. Our new data confirm these previous findings and strengthen previous suggestions that the south-western ridge is colder and denser than, but in approximate pressure equilibrium with, the surrounding ICM atmosphere. In addition, we find evidence for a weak shock that wraps around the north and east sides of the cavity structure. Our data allow us to map the 2-dimensional distribution of metals in the ICM of A4059 for the first time. We find that the SW ridge possesses an anomalously high (super-solar) metalicity. The unusual morphology, temperature structure and metal distribution all point to significant asymmetry in the ICM atmosphere prior to the onset of radio-galaxy activity. Motivated by the very high metalicity of the SW ridge, we hypothesize that the ICM asymmetry was caused by the extremely rapid stripping of metal enriched gas from a starburst galaxy that plunged through the core of A4059. Furthermore, we suggest that the onset of powerful radio-galaxy activity in the cD galaxy may have been initiated by this starburst/stripping event, either via the tidal-shocking of cold gas native to the cD galaxy, or the accretion of cold gas that had been stripped from the starburst galaxy.Comment: Accepted for publication in the Astrophysical Journal. 12 pages, 11 figures. A version of this paper including full resolution figures can be found at http://www.astro.umd.edu/~chris/publications/papers/a4059_2008.pd

Experiments on the stability and transition of two-dimensional and three-dimensional boundary layers with suction

The preliminary experimental development work directed towards the understanding of transition in boundary layers with suction is presented. The basic stability experiment was established and the facility was certified