6,188 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
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
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
A magnified glance into the dark sector: probing cosmological models with strong lensing in A1689
In this paper we constrain four alternative models to the late cosmic
acceleration in the Universe: Chevallier-Polarski-Linder (CPL), interacting
dark energy (IDE), Ricci holographic dark energy (HDE), and modified polytropic
Cardassian (MPC). Strong lensing (SL) images of background galaxies produced by
the galaxy cluster Abell are used to test these models. To perform this
analysis we modify the LENSTOOL lens modeling code. The value added by this
probe is compared with other complementary probes: Type Ia supernovae (SNIa),
baryon acoustic oscillations (BAO), and cosmic microwave background (CMB). We
found that the CPL constraints obtained of the SL data are consistent with
those estimated using the other probes. The IDE constraints are consistent with
the complementary bounds only if large errors in the SL measurements are
considered. The Ricci HDE and MPC constraints are weak but they are similar to
the BAO, SNIa and CMB estimations. We also compute the figure-of-merit as a
tool to quantify the goodness of fit of the data. Our results suggest that the
SL method provides statistically significant constraints on the CPL parameters
but weak for those of the other models. Finally, we show that the use of the SL
measurements in galaxy clusters is a promising and powerful technique to
constrain cosmological models. The advantage of this method is that
cosmological parameters are estimated by modelling the SL features for each
underlying cosmology. These estimations could be further improved by SL
constraints coming from other galaxy clusters.Comment: 13 pages, 5 figures, accepted for publication in Ap
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