9,588 research outputs found
On the outburst evolution of H1743-322: a 2008/2009 comparison
We present two observational campaigns performed with the RXTE satellite on
the black hole transient H 1743-322. The source was observed in outburst on two
separate occasions between October-November 2008 and May-July 2009. We have
carried out timing and spectral analysis of the data set, obtaining a complete
state classification of all the observations. We find that all the observations
are well described by using a spectral model consisting of a disk-blackbody, a
powerlaw + reflection + absorption and a gaussian emission component. During
the 2009 outburst the system followed the canonical evolution through all the
states seen in black hole transients. In the 2008 outburst only the hard states
were reached. The early evolution of the spectral parameters is consistent
between the two epochs, and it does not provide clues about the subsequent
behavior of the source. The variation of the flux associated to the two main
spectral components (i.e. disk and powerlaw) allows us to set a lower limit to
the orbital inclination of the system of >= 43{\deg}.Comment: 13 pages, 5 figures. Accepted for publication in MNRA
Radio-loudness in black hole transients: evidence for an inclination effect
Accreting stellar-mass black holes appear to populate two branches in a
radio:X-ray luminosity plane. We have investigated the X-ray variability
properties of a large number of black hole low-mass X-ray binaries, with the
aim of unveiling the physical reasons underlying the radio-loud/radio-quiet
nature of these sources, in the context of the known accretion-ejection
connection. A reconsideration of the available radio and X-ray data from a
sample of black hole X-ray binaries confirms that being radio-quiet is the more
normal mode of behaviour for black hole binaries. In the light of this we chose
to test, once more, the hypothesis that radio loudness could be a consequence
of the inclination of the X-ray binary. We compared the slope of the
`hard-line' (an approximately linear correlation between X-ray count rate and
rms variability, visible in the hard states of active black holes), the orbital
inclination, and the radio-nature of the sources of our sample. We found that
high-inclination objects show steeper hard-lines than low-inclination objects,
and tend to display a radio-quiet nature (with the only exception of V404 Cyg),
as opposed to low-inclination objects, which appear to be radio-loud(er). While
in need of further confirmation, our results suggest that - contrary to what
has been believed for years - the radio-loud/quiet nature of black-hole low
mass X-ray binaries might be an inclination effect, rather than an intrinsic
source property. This would solve an important issue in the context of the
inflow-outflow connection, thus providing significant constraints to the models
for the launch of hard-state compact jets.Comment: 16 pages, 6 figures, accepted for pubblication on MNRA
Fast variability as a tracer of accretion regimes in black hole transients
We present the rms-intensity diagram for black hole transients. Using
observations taken with the Rossi X-ray timing explorer we study the relation
between the root mean square (rms) amplitude of the variability and the net
count-rate during the 2002, 2004 and 2007 outbursts of the black hole X-ray
binary GX 339-4. We find that the rms-flux relation previously observed during
the hard state in X-ray binaries does not hold for the other states, when
different relations apply. These relations can be used as a good tracer of the
different accretion regimes. We identify the hard, soft and intermediate states
in the rms-intensity diagram. Transitions between the different states are seen
to produce marked changes in the rms-flux relation. We find that one single
component is required to explain the ~ 40 per cent variability observed at low
count rates, whereas no or very low variability is associated to the
accretion-disc thermal component.Comment: Accepted for publication in MNRAS. 6 pages, 4 figure
Imaginary Time Correlations and the phaseless Auxiliary Field Quantum Monte Carlo
The phaseless Auxiliary Field Quantum Monte Carlo method provides a well
established approximation scheme for accurate calculations of ground state
energies of many-fermions systems. Here we apply the method to the calculation
of imaginary time correlation functions. We give a detailed description of the
technique and we test the quality of the results for static and dynamic
properties against exact values for small systems.Comment: 13 pages, 6 figures; submitted to J. Chem. Phy
Energy conservation property of MW-CRF deterministic particle method
AbstractA deterministic particle method for kinetic equation in several dimensions was presented by Motta and Wick some years ago. In the present paper, we formulate the method in general coordinates and apply this formulation to an elastic collision kernel. We show that the method preserves exactly the energy conservation property of the elastic kernel
Spectral variability in Swift and Chandra observations of the Ultraluminous source NGC 55 ULX1
NGC 55 ULX1 is a bright Ultraluminous X-ray source located 1.78 Mpc away. We
analysed a sample of 20 Swift observations, taken between 2013 April and
August, and two Chandra observations taken in 2001 September and 2004 June. We
found only marginal hints of a limited number of dips in the light curve,
previously reported to occur in this source, although the uncertainties due to
the low counting statistics of the data are large. The Chandra and Swift
spectra showed clearly spectral variability which resembles those observed in
other ULXs. We can account for this spectral variability in terms of changes in
both the normalization and intrinsic column density of a two-components model
consisting of a blackbody (for the soft component) and a multicolour accretion
disc (for the hard component). We discuss the possibility that strong outflows
ejected by the disc are in part responsible for such spectral changes.Comment: 9 pages, 6 figure; accepted to be published on MNRA
Approaches to Semantic Web Services: An Overview and Comparison
Abstract. The next Web generation promises to deliver Semantic Web Services (SWS); services that are self-described and amenable to automated discovery, composition and invocation. A prerequisite to this, however, is the emergence and evolution of the Semantic Web, which provides the infrastructure for the semantic interoperability of Web Services. Web Services will be augmented with rich formal descriptions of their capabilities, such that they can be utilized by applications or other services without human assistance or highly constrained agreements on interfaces or protocols. Thus, Semantic Web Services have the potential to change the way knowledge and business services are consumed and provided on the Web. In this paper, we survey the state of the art of current enabling technologies for Semantic Web Services. In addition, we characterize the infrastructure of Semantic Web Services along three orthogonal dimensions: activities, architecture and service ontology. Further, we examine and contrast three current approaches to SWS according to the proposed dimensions
- …