5,089 research outputs found
Echo-Mapping of Swift J1753.5-0127
We present two epochs of coordinated X-ray-optical timing observations of the
black hole candidate Swift J1753.5-0127 during its 2005 outburst. The first
epoch in July occurred at outburst peak. Two consecutive nights of observations
using the McDonald Observatory Argos camera with the Rossi X-ray Timing
Explorer show a consistent correlation with an immediate response and an
extended tail lasting ~5s. The properties of the variability and the
correlation are consistent with thermal reprocessing in an accretion disk. The
shortness of the lag suggests a short orbital period consistent with that
recently claimed. The second epoch in August used the VLT FORS2 HIT mode again
in conjunction with RXTE. Again a repeatable correlation is seen between two
independent subsets of the data. In this case, though, the cross-correlation
function has an unusual structure comprising a dip followed by a double-peak.
We suggest that this may be equivalent to the dip plus single peak structure
seen by Kanbach et al. (2001) in XTE J1118+480 and attributed there to
synchrotron emission; a similar structure was seen during later activity of
Swift J1753.5-0127 by Durant et al. (2008).Comment: 7 pages, accepted for publication in Monthly Notices of the Royal
Astronomical Societ
A continental rift model for the La Grande greenstone belt
Stratigraphic relationships and the geochemistry of volcanic rocks contrain the nature and timing of the tectonic and magmatic processes in the pre-deformational history of the La Grande greenstone belt in the Superior Province of north-central Quebec. The lowermost supracrustals in this belt are obscured by syntectonic granitoid intrusives. The supracrustal succession in the western part of the belt consists of a lower sequence of immature clastic sediments and mafic volcanoclastics, overlain by pillowed and massive basalts. Further east, along tectonic strike, a lower sequence of mafic volcanoclastics and immature clastic sediments is overlain by a thick sequence of pillowed and massive basalts, and resedimented coarse clastic sediments and banded iron formation. These are overlain by assive basaltic andesites, andesites and intermediate volcanoclastics intercalated with immature clastic sediments. In contrast, in the eastern part of the belt lenses of felsic volcanics and volcanoclastics occur at the base of the succession and pillowed and massive basalts are overlain by komatiites at the top. The La Grande greenstone belt can be explained as the product of continental rifting. The restricted occurence of komatiites, and eastwardly directed paleocurrents in clastic sediments in the central part of the belt are consistent with rifting commencing in the east and propagating westward with time. The increase in depth of emplacement and deposition with time of the lower three units in the central part of the belt reflects deposition in a subsiding basin. These supracrustal rocks are believed to represent the initial rift succession
On the Optical -- X-ray correlation from outburst to quiescence in Low Mass X-ray Binaries: the representative cases of V404 Cyg and Cen X-4
Low mass X-ray binaries (LMXBs) show evidence of a global correlation of
debated origin between X-ray and optical luminosity. We study for the first
time this correlation in two transient LMXBs, the black hole V404 Cyg and the
neutron star Cen X-4, over 6 orders of magnitude in X-ray luminosity, from
outburst to quiescence. After subtracting the contribution from the companion
star, the Cen X-4 data can be described by a single power law correlation of
the form , consistent with disk reprocessing. We
find a similar correlation slope for V404 Cyg in quiescence (0.46) and a
steeper one (0.56) in the outburst hard state of 1989. However, V404 Cyg is
about times optically brighter, at a given keV X-ray
luminosity, compared to Cen X-4. This ratio is a factor of 10 smaller in
quiescence, where the normalization of the V404 Cyg correlation also changes.
We show that once the bolometric X-ray emission is considered and the known
main differences between V404 Cyg and Cen X-4 are taken into account (a larger
compact object mass, accretion disk size, and the presence of a strong jet
contribution in the hard state for the black hole system) the two systems lie
on the same correlation. In V404 Cyg, the jet dominates spectrally at
optical-infrared frequencies during the hard state, but makes a negligible
contribution in quiescence, which may account for the change in its correlation
slope and normalization. These results provide a benchmark to compare with data
from the 2015 outburst of V404 Cyg and, potentially, other transient LMXBs as
well.Comment: Accepted on ApJ, 12 pages, 4 figures, 4 table
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Effect of clocking on compressor noise generation
The effect of stator clocking on the acoustic noise generation characteristics in an axial high-pressure compressor is analysed. A realistic geometry with one-and-a-half stages is assessed using high fidelity and low-order numerical methods for different clocking positions at approach operating conditions.
The compressor efficiency and the acoustic noise emission is found to vary insignificantly between the simulated clocking configurations. Nonetheless, the pressure distribution is altered significantly right upstream of the inlet guide vanes. Although the cut-on modes exhibit at least 10 dB higher amplitudes, the cut-off modes contribute decisively to the wave pattern in the near field. Optimal acoustic liner design can expand on the differently evolving interference pattern of acoustic waves at discrete frequencies.
The low-order model is found to predict the directionality of the acoustic waves and the cut-on criteria for the individual modes in excellent agreement with the high fidelity simulations. However, the phase cannot be estimated due to the simplicity of the low-order formulation.The authors wish to express their sincere gratitude to Rolls-Royce plc for the permission to publish this paper, which partly developed through the Rolls-Royce plc and Innovate UK Aerospace Technology Institute funded research programme, ACAPELLA
Multiwavelength Observations of Swift J1753.5-0127
We present contemporaneous X-ray, ultraviolet, optical and near-infrared
observations of the black hole binary system, Swift J1753.5-0127, acquired in
2012 October. The UV observations, obtained with the Cosmic Origins
Spectrograph on the Hubble Space Telescope, are the first UV spectra of this
system. The dereddened UV spectrum is characterized by a smooth, blue continuum
and broad emission lines of CIV and HeII. The system was stable in the UV to
<10% during our observations. We estimated the interstellar reddening by
fitting the 2175 A absorption feature and fit the interstellar absorption
profile of Ly to directly measure the neutral hydrogen column density
along the line of sight. By comparing the UV continuum flux to steady-state
thin accretion disk models, we determined upper limits on the distance to the
system as a function of black hole mass. The continuum is well fit with disk
models dominated by viscous heating rather than irradiation. The broadband
spectral energy distribution shows the system has declined at all wavelengths
since previous broadband observations in 2005 and 2007. If we assume that the
UV emission is dominated by the accretion disk the inner radius of the disk
must be truncated at radii above the ISCO to be consistent with the X-ray flux,
requiring significant mass loss from outflows and/or energy loss via advection
into the black hole to maintain energy balance.Comment: To appear in the Ap
A STOL airworthiness investigation using a simulation of a deflected slipstream transport. Volume 1: Summary of results and airworthiness implications
A simulator study of short takeoff and landing (STOL) aircraft was conducted using a model of a deflected slipstream transport aircraft. The subjects considered are: (1) the approach, (2) flare and landing, (3) go-around, and (4) takeoff phases of flight. The results are summarized and possible implications with regard to airworthiness criteria are discussed. A data base is provided for future STOL airworthiness requirements and a preliminary indication of potential problem areas is developed. Comparison of the simulation results with various proposed STOL criteria indicates significant deficiencies in many of these criteria
Examining biochar as a carrier for Rhizobium spp. on pea crop
Non-Peer Reviewe
Anti-correlated Soft Lags in the Intermediate State of Black Hole Source GX 339-4
We report the few hundred second anti-correlated soft lags between soft and
hard energy bands in the source GX 339-4 using RXTE observations. In one
observation, anti-correlated soft lags were observed using the ISGRI/INTEGRAL
hard energy band and the PCA/RXTE soft energy band light curves. The lags were
observed when the source was in hard and soft intermediate states, i.e., in a
steep power-law state.We found that the temporal and spectral properties were
changed during the lag timescale. The anti-correlated soft lags are associated
with spectral variability during which the geometry of the accretion disk is
changed. The observed temporal and spectral variations are explained using the
framework of truncated disk geometry. We found that during the lag timescale,
the centroid frequency of quasi-periodic oscillation is decreased, the soft
flux is decreased along with an increase in the hard flux, and the power-law
index steepens together with a decrease in the disk normalization parameter. We
argue that these changes could be explained if we assume that the hot corona
condenses and forms a disk in the inner region of the accretion disk. The
overall spectral and temporal changes support the truncated geometry of the
accretion disk in the steep power-law state or in the intermediate state.Comment: published in ApJ, 9 pages, 8 figure
Properties of the propagating shock wave in the accretion flow around GX 339-4 in the 2010 outburst
Context. The black hole candidate GX 339-4 exhibited an X-ray outburst in
January 2010, which is still continuing. We here discuss the timing and the
spectral properties of the outburst using RXTE data. Aims. Our goal is to study
the timing and spectral properties of GX 339-4 using its recent outburst data
and extract information about the nature of the accretion flow. Methods. We use
RXTE archival data of the recent GX 339-4 outburst and analyze them with the
NASA HEAsoft package, version 6.8. We then compare the observed quasi-periodic
oscillation (QPO) frequencies with those from existing shock oscillation model
and obtain the nature of evolution of the shock locations during the outburst.
Results. We found that the QPO frequencies are monotonically increasing from
0.102 Hz to 5.69 Hz within a period of ~ 26 days. We explain this evolution
with the propagating oscillatory shock (POS) solution and find the variation of
the initial and final shock locations and strengths. The model fits also give
the velocity of the propagating shock wave, which is responsible for the
generation of QPOs and their evolutions, at ~ 10 m/s. We observe from the
spectra that up to 2010 April 10, the object was in a hard state. After that,
it went to the hard-intermediate state. On April 18, it had a state transition
and went to the soft-intermediate state. On May 15, another state transition
was observed and the source moved to the soft state. Conclusions. As in the
previously fitted outburst sources, this source also showed the tendency of a
rapidly increasing QPO frequency () in a viscous time scale, which
can be modeled quite accurately. In this case, the shock seems to have
disappeared at about ~ 172 Schwarzschild radii, unlike in the 2005 outburst of
GRO J1655-40, where the shock disappeared behind the horizon.Comment: 5 pages, 5 figures, two tales (accepted for publication in A & A
Journal
A STOL airworthiness investigation using a simulation of an augmentor wing transport. Volume 2: Simulation data and analysis
A simulator study of STOL airworthiness was conducted using a model of an augmentor wing transport. The approach, flare and landing, go-around, and takeoff phases of flight were investigated. The simulation and the data obtained are described. These data include performance measures, pilot commentary, and pilot ratings. A pilot/vehicle analysis of glide slope tracking and of the flare maneuver is included
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