1,444 research outputs found
Wide band observations of the X-ray burster GS 1826-238
GS 1826-238 is a well-studied X-ray bursting neutron star in a low mass
binary system. Thermal Comptonisation by a hot electron cloud is a widely
accepted mechanism accounting for its high energy emission, while the nature of
most of its soft X-ray output is not completely understood. A further low
energy component is typically needed to model the observed spectra: pure
blackbody and Comptonisation-modified blackbody radiation by a lower
temperature (a few keV) electron plasma were suggested to explain the low
energy data. We studied the steady emission of GS 1826-238 by means of broad
band (X to soft Gamma-rays) measurements obtained by the INTEGRAL observatory
in 2003 and 2006. The newly developed, up-to-date Comptonisation model CompTB
is applied for the first time to study effectively the low-hard state
variability of a low-luminosity neutron star in a low-mass X-ray binary system.
We confirm that the 3-200 keV emission of \GS is characterised by
Comptonisation of soft seed photons by a hot electron plasma. A single spectral
component is sufficient to model the observed spectra. At lower energies, no
direct blackbody emission is observed and there is no need to postulate a low
temperature Compton region. Compared to the 2003 measurements, the plasma
temperature decreased from 20 to 14 keV in 2006, together with the seed photons
temperature. The source intensity was also found to be 30% lower in 2006,
whilst the average recurrence frequency of the X-ray bursts significantly
increased. Possible explanations for this apparent deviation from the typical
limit-cycle behaviour of this burster are discussed.Comment: 6 pages, 2 figures. Accepted for publication in A&
Continuous Veno-Venous Hemodialysis Using the Cardio-Renal Pediatric Dialysis Emergency Machine TM : First Clinical Experiences
Effect of holes arrangement on heat transfer in impingement/effusion cooling double wall schemes
Bright X-ray bursts from 1E 1724-3045 in Terzan 2
During about 3 years wide field monitoring of the Galactic Center region by
the WFC telescopes on board the BeppoSAX satellite, a total of 14 type-I X-ray
bursts were detected from the burster 1E 1724-3045 located in the globular
cluster Terzan 2. All the observed events showed evidence for photospheric
radius expansion due to Eddington-limit burst luminosity, thus leading to an
estimate of the source distance (~7.2 kpc). Preliminary results of the analysis
of the bursts are presented.Comment: 5 pages, 2 figures, Proc. 5th Compton Symp., Portsmouth 199
Potential-field inversion for a layer with uneven thickness: the Tyrrhenian Sea density model
Inversion of large-scale potential-field anomalies, aimed at determining density or magnetization, is usually made in the Fourier domain. The commonly adopted geometry is based on a layer of constant thickness, characterized by a bottom surface at a fixed distance from the top surface. We propose a new method to overcome this limiting geometry, by inverting in the usual iterating scheme using top and bottom surfaces of differing, but known shapes. Randomly generated synthetic models will be analyzed, and finally performance of this method will be tested on real gravity data describing the isostatic residual anomaly of the Southern Tyrrhenian Sea in Italy. The final result is a density model that shows the distribution of the oceanic crust in this region, which is delimited by known structural elements and appears strongly correlated with the oceanized abyssal basins of Vavilov and Marsili
Detph-to-the-bottom Optimization for Potential-field Data Inversion
We show an algorithm for the linear inversion of 2D surface magnetic data to obtain 3D models of the susceptibility of the source. After showing a novel characterization of the ambiguity domain in the Fourier space, which has a simple geometrical interpretation, we will demonstrate that a depth-weighting function is useful to significantly reduce the ambiguity domain in order to characterize the main source properties. The forward model is discretized by a mesh of prismatic cells with constant magnetization that allows the recovery of a complete 3D generating source. As the number of cells are normally grater than the amount of available data, we are left with an underdetermined linear inverse problem, which can be regularized in order to obtain an unique solution by a depth-weighting function, adapted from Li and Oldenburg (1996) to close the source towards its bottom. The main novelty of this method is a first-stage optimization that gives information about the depth-to-the-bottom (dtb) of the generating source. This parameter permits both the evaluation of the appropriate vertical extension of the mesh, and the definition of the shape of the regularizing depth-weighting distribution. The adopted method is suitable under appropriate changes to deal also with gravity data. After showing which kind of a priori information is introduced by this particular regularization, we will describe its limits and its possible improvements and then we will show the results of some synthetic tests. As a final application we will show the 3D magnetic model of an interesting volcanic region in Italy
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