1,722,659 research outputs found
Intermittent millisecond x-ray pulsations from the neutron star x-ray transient SAX J1748.9-2021 in the globular cluster NGC 6440
No full textWe report on intermittent X-ray pulsations with a frequency of 442.36 Hz from the neutron-star X-ray binary SAX J1748.9-2021 in the globular cluster NGC 6440. The pulsations were seen during both 2001 and 2005 outbursts of the source, but only intermittently, appearing and disappearing on timescales of hundreds of seconds. We find a suggestive relation between the occurrence of type-I X-ray bursts and the appearance of the pulsations but the relation is not strict. This behavior is very similar to that of the intermittent accreting millisecond X-ray pulsar HETE J1900.1-2455. The reason for the intermittence of the pulsations remains unclear. However it is now evident that a strict division between pulsating and non-pulsating does not exist. By studying the Doppler shift of the pulsation frequency we determine an orbit with a period of 8.7 hrs and an projected semi major axis of 0.39 lightsec. The companion star might be a main-sequence or a slightly evolved star with a mass of ~1 Msun. Therefore, SAX J1748.9-2021 has a longer period and may have a more massive companion star than all the other accreting millisecond X-ray pulsars except for Aql X-1
Letter to Nature: An ultra-relativistic outflow from a neutron star accreting gas from a companion.
No full textCollimated relativistic outflows—also known as jets—are amongst the most energetic phenomena in the Universe. They are associated with supermassive black holes in distant active galactic nuclei1, accreting stellar-mass black holes and neutron stars in binary systems2 and are believed to be responsible for gamma-ray bursts3. The physics of these jets, however, remains something of a mystery in that their bulk velocities, compositions and energetics remain poorly determined. Here we report the discovery of an ultra-relativistic outflow from a neutron star accreting gas within a binary stellar system. The velocity of the outflow is comparable to the fastest-moving flows observed from active galactic nuclei, and its strength is modulated by the rate of accretion of material onto the neutron star. Shocks are energized further downstream in the flow, which are themselves moving at mildly relativistic bulk velocities and are the sites of the observed synchrotron emission from the jet. We conclude that the generation of highly relativistic outflows does not require properties that are unique to black holes, such as an event horizon
Physico - chemical chyme conditions and mineral absorption in broilers
No full text In the Netherlands the efficiency of mineral absorption from the gastrointestinal tract of farm animals is a topic of interest to reduce the mineral concentration in animal manure. This study was done with broilers. It was focused on physico-chemical chyme conditions. These conditions were related to the absorption of minerals. Carboxy methyl cellulose was used as a model substance to affect the intestinal viscosities. Retention time parameters, pH and osmolalities were recorded. The site of mineral (Na, K, Ca, P, and Mg) absorption and apparent absorption values up to successive gastrointestinal segments were determined. Effects of the intestinal viscosity were verified using wheat-based broiler diets.Dietary inclusion of carboxy methyl cellulose (up to 1%) increased the intestinal viscosity, the mean retention time and decreased the ileal pH. The absorption of small osmo-active chyme components was reduced, which was reflected in less variable osmolalities as the chyme moved from the proximal small intestine onwards. The main site of mineral absorption is between the duodenum and the lower jejunum. In these segments the absorption is negatively affected by the inclusion of carboxy methyl cellulose in the diet. It was discussed that the intestinal viscosity was the main cause for this reduction in mineral absorption. Negative effects were partially compensated in the ileum. Similar effects were shown in wheat-based diets, but effects were less pronounced
Cosmic recycling of millisecond pulsars
No full textWe compare the rotation rate of neutron stars in low-mass X-ray binaries (LMXBs) with the orbital period of the binaries. We find that, while short orbital period LMXBs span a range of neutron star rotation rates, all the long-period LMXBs have fast rotators. We also find that the rotation rates are highest for the systems with the highest mean mass accretion rates, as can be expected if the accretion rate correlates with the orbital period. We show that these properties can be understood by a balance between spin-up due to accretion and spin-down due to gravitational radiation. Our scenario indicates that the gravitational radiation emitted by these systems may be detectable by future ground-based gravitational wave detector
Discovery of a 205.89 Hz accreting millisecond x-ray pulsar in the globular cluster NGC 6440
No full textWe report on the discovery of the second accreting millisecond X-ray pulsar (AMXP) in the globular cluster NGC 6440. Pulsations with a frequency of 205.89 Hz were detected with RXTE on 2009 August 30, October 1 and October 28, during the decays of 4 day outbursts of a newly X-ray transient source in NGC 6440. By studying the Doppler shift of the pulsation frequency, we find that the system is an ultra-compact binary with an orbital period of 57.3 minutes and a projected semimajor axis of 6.22 lt-ms. Based on the mass function, we estimate a lower limit to the mass of the companion to be 0.0067 M ? (assuming a 1.4 M ? neutron star). This new pulsar shows the shortest outburst recurrence time among AMXPs (~1 month). If this behavior does not cease, this AMXP has the potential to be one of the best sources in which to study how the binary system and the neutron star spin evolve. Furthermore, the characteristics of this new source indicate that there might exist a population of AMXPs undergoing weak outbursts which are undetected by current all-sky X-ray monitors. NGC 6440 is the only globular cluster to host two known AMXPs, while no AMXPs have been detected in any other globular cluster
GX 339-4:Back to life
No full textAfter almost three years of quiescence, the ``persistent" BHC GX 339-4 became active again on 2002 March 26 (Smith, et al. 2002). This source is important , as in the past it has shown in the past all of the ``canonical'' states of BHCs (Méndez & van der Klis, 1997)
Expert opinion: uncertainties in hydraulic roughness
Get PDFWater level predictions in rivers are used for a variety of purposes in water management. For example, designing flood defence measures and evaluating natural rehabilitation in flood plains, cannot be done without water level predictions. However, these water level predictions are uncertain and a major part of this uncertainty is caused by the uncertainty in the roughness coefficient (Van der Klis, 2003; Van Vuren, 2005). Hydraulic roughness in rivers results from (among others): grain roughness, form roughness and vegetation roughness. The roughness coefficient is uncertain because different elements creating the hydraulic roughness are uncertain (e.g. grain size, dune height). To quantify the influence of the uncertain roughness coefficient on water level predictions, we first need a quantification of the uncertainty in the roughness coefficient
Tomographic reflection modelling of quasi-periodic oscillations in the black hole binary H 1743–322
Get PDFAccreting stellar mass black holes (BHs) routinely exhibit Type-C quasi-periodic oscillations (QPOs). These are often interpreted as Lense–Thirring precession of the inner accretion flow, a relativistic effect whereby the spin of the BH distorts the surrounding space–time, inducing nodal precession. The best evidence for the precession model is the recent discovery, using a long joint XMM–Newton and NuSTAR observation of H 1743−322, that the centroid energy of the iron florescence line changes systematically with QPO phase. This was interpreted asthe inner flow illuminating different azimuths of the accretion disc as it precesses, giving rise to a blueshifted/redshifted iron line when the approaching/receding disc material is illuminated. Here, we develop a physical model for this interpretation, including a self-consistent reflection continuum, and fit this to the same H 1743−322 data. We use an analytic function to parametrize the asymmetric illumination pattern on the disc surface that would result from inner flow precession, and find that the data are well described if two bright patches rotate about the disc surface. This model is preferred to alternatives considering an oscillating disc ionization parameter, disc inner radius and radial emissivity profile. We find that the reflection fraction varies with QPO phase (3.5σ), adding to the now formidable body of evidence thatType-C QPOs are a geometric effect. This is the first example of tomographic QPO modelling, initiating a powerful new technique that utilizes QPOs in order to map the dynamics of accreting material close to the BH
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