118 research outputs found
Evidence for different accretion regimes in GRO J1008-57
We present a comprehensive spectral analysis of the BeXRB GRO J1008-57 over a
luminosity range of three orders of magnitude using NuSTAR, Suzaku and RXTE
data. We find significant evolution of the spectral parameters with luminosity.
In particular the photon index hardens with increasing luminosity at
intermediate luminosities between erg s. This
evolution is stable and repeatedly observed over different outbursts. However,
at the extreme ends of the observed luminosity range, we find that the
correlation breaks down, with a significance level of at least . We
conclude that these changes indicate transitions to different accretion
regimes, which are characterized by different deceleration processes, such as
Coulomb or radiation breaking. We compare our observed luminosity levels of
these transitions to theoretical predications and discuss the variation of
those theoretical luminosity values with fundamental neutron star parameters.
Finally, we present detailed spectroscopy of the unique "triple peaked"
outburst in 2014/15 which does not fit in the general parameter evolution with
luminosity. The pulse profile on the other hand is consistent with what is
expected at this luminosity level, arguing against a change in accretion
geometry. In summary, GRO J1008-57 is an ideal target to study different
accretion regimes due to the well constrained evolution of its broad-band
spectral continuum over several orders of magnitude in luminosity.Comment: 13 pages, 7 figures, 3 tables. Accepted for publication in A&
Observation of crystallization slowdown in supercooled para-hydrogen and ortho-deuterium quantum liquid mixtures
We report a quantitative experimental study of the crystallization kinetics
of supercooled quantum liquid mixtures of para-hydrogen (pH) and
ortho-deuterium (oD) by high spatial resolution Raman spectroscopy of
liquid microjets. We show that in a wide range of compositions the
crystallization rate of the isotopic mixtures is significantly reduced with
respect to that of the pure substances. To clarify this behavior we have
performed path-integral simulations of the non-equilibrium pH-oD liquid
mixtures, revealing that differences in quantum delocalization between the two
isotopic species translate into different effective particle sizes. Our results
provide first experimental evidence for crystallization slowdown of quantum
origin, offering a benchmark for theoretical studies of quantum behavior in
supercooled liquids.Comment: 6 pages, 3 figure
EXO 2030+375 Restarts in Reverse
The Be X-ray binary pulsar EXO 2030+375, first detected in 1985, has shown a
significant detected X-ray outburst at nearly every periastron passage of its
46-day orbit for the past ~25 years, with one low state accompanied by a torque
reversal in the 1990s. In early 2015 the outbursts progressively became fainter
and less regular while the monotonic spin-up flattened. At the same time a
decrease in the H line equivalent width was reported, indicating a
change in the disk surrounding the mass donor.
In order to explore the source behaviour in the poorly explored low-flux
state with a possible transition to a state of centrifugal inhibition of
accretion we have undertaken an observing campaign with Swift/XRT, NuSTAR and
the Nordic Optical Telescope (NOT). This conference contribution reports the
preliminary results obtained from our campaign.Comment: 11th INTEGRAL Conference Gamma-Ray Astrophysics in Multi-Wavelength
Perspective, 10-14 October 2016, Amsterdam, The Netherlands. 7 page
Experiments on microjets of undercooled liquid hydrogen
28th International Symposium on Rarefied Gas Dynamics 2012 (2012). AIP Conf. Proc.; 9 pags. ; 7 figs. ; 1 tab. ; PACS: 67.63.Cd, 33.20.Fb, 64.60.My, 64.70.dg, 47.60.KzNovel experiments on liquid microjets (filaments) of hydrogen and deuterium, carried out at the Laboratory of
Molecular Fluid Dynamics of the IEM, are reported. These filaments, less than 10 microns in diameter, are an ideal medium
to produce highly undercooled liquid samples and to investigate the homogeneous solidification process, free from wall
effects. The filaments exit from cryogenic capillary nozzles into a vacuum chamber, to cool down very fast by surface evaporation. Finite size radius leads to a temperature gradient across the filament, determined by thermal conductivity, and, possibly, to a velocity gradient as well. The filaments are monitored by laser shadowgraphy, and analyzed by means of high performance Raman spectroscopy. Real-time measurements in the rotational and vibrational spectral regions reveal the structure and temperature along the filaments, allowing to track the crystal growth process. The high spatial resolution of Raman spectroscopy allows observing in situ the structural changes of the liquid microjets, with a time resolution of ∼ 10
ns. The filaments of pure para-H2 can be cooled down to 9 K (65% of its melting point at 13.8 K), while staying liquid,
before eventually solidifying into a metastable polymorph. Crystallization kinetics revealed a growth rate of 33 cm/s, much higher than expected for a thermally activated process. The time and spatial control attained in these experiments offers new opportunities for investigating the processes of nonequilibrium phase transformations in undercooled fluids, as well as the propagation of liquid jets into a rarefied gas media. © 2012 American Institute of PhysicsThis work has been supported by the the Spanish Ministerio de Ciencia e Innovacion, through grants FIS2007-61430, FIS2010-22064-C02-01, and HD2008-0068, by the Helmholtz Gemeinschaft, through grant VH-NG-331, and by the German academic exchange service (DAAD) under reference Nr. 50025171.Peer reviewe
Metal uptake and distribution in the zebrafish (Danio rerio) embryo: differences between nanoparticles and metal ions
Quantitative data on nanoparticle and cation uptake are compared in a compartment-specific way and distinct differences between metals were identified
The accretion environment in Vela X-1 during a flaring period using XMM-Newton
We present analysis of 100 ks contiguous XMM-Newton data of the prototypical
wind accretor Vela X-1. The observation covered eclipse egress between orbital
phases 0.134 and 0.265, during which a giant flare took place, enabling us to
study the spectral properties both outside and during the flare. This giant
flare with a peak luminosity of erg
s allows estimates of the physical parameters of the accreted structure
with a mass of g.
We have been able to model several contributions to the observed spectrum
with a phenomenological model formed by three absorbed power laws plus three
emission lines. After analysing the variations with orbital phase of the column
density of each component, as well as those in the Fe and Ni fluorescence
lines, we provide a physical interpretation for each spectral component.
Meanwhile, the first two components are two aspects of the principal accretion
component from the surface of the neutron star, and the third component seems
to be the \textit{X-ray light echo} formed in the stellar wind of the
companion.Comment: Accepted. Astronomy and Astrophysics, 201
Observations of the High-mass X-Ray Binary A 0535+26 in Quiescence
We have analyzed three observations of the high-mass X-ray binary A 0535+26 performed by the Rossi X-Ray Timing Explorer (RXTE) three, five, and six months after the last outburst in 2011 February. We detect pulsations only in the second observation. The 3-20 keV spectra can be fit equally well with either an absorbed power law or absorbed thermal bremsstrahlung model. Reanalysis of two earlier RXTE observations made 4 yr after the 1994 outburst, original BeppoSAX observations 2 yr later, reanalysis of four EXOSAT observations made 2 yr after the last 1984 outburst, and a recent XMM-Newton observation in 2012 reveal a stacked, quiescent flux level decreasing from ~2 to <1 × 10^(–11) erg cm^(–2) s^(–1) over 6.5 yr after outburst. The detection of pulsations during half of the quiescent observations would imply that accretion onto the magnetic poles of the neutron star continues despite the fact that the circumstellar disk may no longer be present. The accretion could come from material built up at the corotation radius or from an isotropic stellar wind
Discovery and modelling of a flattening of the positive cyclotron line/luminosity relation in GX 304−1 with RXTE
The Rossi X-ray Timing Explorer (RXTE) observed four outbursts of the accreting X-ray binary transient source, GX 304−1 in 2010 and 2011. We present results of detailed 3–100 keV spectral analysis of 69 separate observations, and report a positive correlation between cyclotron line parameters, as well as other spectral parameters, with power-law flux. The cyclotron line energy, width and depth versus flux, and thus luminosity, correlations show a flattening of the relationships with increasing luminosity, which are well described by quasi-spherical or disc accretion that yield the surface magnetic field to be ∼5 × 10^(12) Gauss. Since HEXTE (High Energy X-ray Timing Experiment) cluster A was fixed aligned with the Proportional Counter Array field of view and cluster B was fixed viewing a background region 1°.5 off of the source direction during these observations near the end of the RXTE mission, the cluster A background was estimated from cluster B events using
HEXTEBACKEST.
This made possible the detection of the ∼55 keV cyclotron line and an accurate measurement of the continuum. Correlations of all spectral parameters with the primary 2–10 keV power-law flux reveal it to be the primary driver of the spectral shape. The accretion is found to be in the collisionless shock braking regime
HIV-1 induces telomerase activity in monocyte-derived macrophages, possibly safeguarding one of its reservoirs
Monocyte-derived macrophages (MDM) are widely distributed in all tissues and organs, including the central nervous system, where they represent the main part of HIV-infected cells. In contrast to activated CD4+ T lymphocytes, MDMare resistant to cytopathic effects and survive HIV infection for a long period of time. The molecular mechanisms of how HIV is able to persist in macrophages are not fully elucidated yet. In this context, we have studied the effect of in vitro HIV-1 infection on telomerase activity (TA), telomere length, and DNA damage. Infection resulted in a significant induction of TA. This increase was directly proportional to the efficacy of HIV infection and was found in both nuclear and cytoplasmic extracts, while neither UV lightinactivated HIV nor exogenous addition of the viral protein Tat or gp120 affected TA. Furthermore, TA was not modified during monocyte-macrophage differentiation, MDMactivation, or infection with vaccinia virus. HIV infection did not affect telomere length. However, HIV-infectedMDMshowed less DNA damage after oxidative stress than noninfected MDM, and this resistance was also increased by overexpressing telomerase alone. Taken together, our results suggest that HIV induces TA inMDMand that this induction might contribute to cellular protection against oxidative stress, which could be considered a viral strategy to make macrophages better suited as longer-lived, more resistant viral reservoirs. In the light of the clinical development of telomerase inhibitors as anticancer therapeutics, inhibition of TA in HIV-infected macrophages might also represent a novel therapeutic target against viral reservoirs.Fil: Reynoso, Rita Paola. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Biomédicas en Retrovirus y Sida. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Biomédicas en Retrovirus y Sida; Argentina. University of Natural Resources and Life Sciences Vienna; AustriaFil: Wieser, Matthias. University of Natural Resources and Life Sciences Vienna; AustriaFil: Ojeda, Diego. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Biomédicas en Retrovirus y Sida. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Biomédicas en Retrovirus y Sida; ArgentinaFil: Bönisch, Maximilian. University of Natural Resources and Life Sciences Vienna; AustriaFil: Kühnel, Harald. University of Natural Resources and Life Sciences Vienna; AustriaFil: Bolcic, Federico Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Biomédicas en Retrovirus y Sida. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Biomédicas en Retrovirus y Sida; ArgentinaFil: Quendler, Heribert. University of Natural Resources and Life Sciences Vienna; AustriaFil: Grillari, Johannes. University of Natural Resources and Life Sciences Vienna; AustriaFil: Grillari Voglauer, Regina. University of Natural Resources and Life Sciences Vienna; AustriaFil: Quarleri, Jorge Fabian. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Biomédicas en Retrovirus y Sida. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Biomédicas en Retrovirus y Sida; Argentin
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