2,281 research outputs found
X-ray Reflection Spectroscopy of the Black Hole GX 339-4: Exploring the Hard State with Unprecedented Sensitivity
We analyze {\it simultaneously} six composite {\it RXTE} spectra of GX 339--4
in the hard state comprising 77 million counts collected over 196 ks. The
source spectra are ordered by luminosity and spanthe range 1.6\% to 17\% of the
Eddington luminosity. Crucially, using our new tool {\tt pcacorr}, we
re-calibrate the data to a precision of 0.1\%, an order of magnitude
improvement over all earlier work. Using our advanced reflection model {\tt
relxill}, we target the strong features in the component of emission reflected
from the disk, namely, the relativistically-broadened Fe K emission line, the
Fe K edge and the Compton hump. We report results for two joint fits to the six
spectra: For the first fit, we fix the spin parameter to its maximal value
() and allow the inner disk radius to vary. Results
include (i) precise measurements of , with evidence that the disk
becomes slightly truncated at a few percent of Eddington; and (ii) an
order-of-magnitude swing with luminosity in the high energy cutoff, which
reaches keV at our lowest luminosity. For the second fit, we make the
standard assumption in estimating spin that the inner edge of the accretion
disk is located at the innermost stable circular orbit () and find (90\% confidence,
statistical). For both fits, and at the same level of statistical confidence,
we estimate that the disk inclination is deg and that the Fe
abundance is super-solar, .Comment: Accepted for publication in ApJ, 20 pages, 13 figure
On Estimating the High-Energy Cutoff in the X-ray Spectra of Black Holes via Reflection Spectroscopy
The fundamental parameters describing the coronal spectrum of an accreting
black hole are the slope of the power-law continuum and the energy
at which it rolls over. Remarkably, this parameter can be accurately
measured for values as high as 1 MeV by modeling the spectrum of X-rays
reflected from a black hole accretion disk at energies below 100 keV. This is
possible because the details in the reflection spectrum, rich in fluorescent
lines and other atomic features, are very sensitive to the spectral shape of
the hardest coronal radiation illuminating the disk. We show that fitting
simultaneous NuSTAR (3-79 keV) and low-energy (e.g., Suzaku) data with the most
recent version of our reflection model RELXILL, one can obtain reasonable
constraints on at energies from tens of keV up to 1 MeV, for a source
as faint as 1 mCrab in a 100 ks observation.Comment: Accepted for publication in ApJL, 6 pages, 5 figure
The Low-Spin Black Hole in LMC X-3
Building upon a new dynamical model for the X-ray binary LMC X-3, we measure
the spin of its black hole primary via the continuum-fitting method. We
consider over one thousand thermal-state RXTE X-ray spectra of LMC X-3. Using a
large subset of these spectra, we constrain the spin parameter of the black
hole to be spin = 0.21(+0.18,-0.22), 90% confidence. Our estimate of the
uncertainty in spin takes into account a wide range of systematic errors. We
discuss evidence for a correlation between a black hole's spin and the
complexity of its X-ray spectrum.Comment: Submitted to ApJL, 5 pages emulateapj, 2 figures and 1 tabl
Modeling the Optical-X-ray Accretion Lag in LMC X-3: Insights Into Black-Hole Accretion Physics
The X-ray persistence and characteristically soft spectrum of the black hole
X-ray binary LMC X-3 make this source a touchstone for penetrating studies of
accretion physics. We analyze a rich, 10-year collection of optical/infrared
(OIR) time-series data in conjunction with all available contemporaneous X-ray
data collected by the ASM and PCA detectors aboard the Rossi X-ray Timing
Explorer. A cross-correlation analysis reveals an X-ray lag of ~2 weeks.
Motivated by this result, we develop a model that reproduces the complex OIR
light curves of LMC X-3. The model is comprised of three components of
emission: stellar light; accretion luminosity from the outer disk inferred from
the time-lagged X-ray emission; and light from the X-ray-heated star and outer
disk. Using the model, we filter a strong noise component out of the
ellipsoidal light curves and derive an improved orbital period for the system.
Concerning accretion physics, we find that the local viscous timescale in the
disk increases with the local mass accretion rate; this in turn implies that
the viscosity parameter alpha decreases with increasing luminosity. Finally, we
find that X-ray heating is a strong function of X-ray luminosity below ~50% of
the Eddington limit, while above this limit X-ray heating is heavily
suppressed. We ascribe this behavior to the strong dependence of the flaring in
the disk upon X-ray luminosity, concluding that for luminosities above ~50% of
Eddington, the star lies fully in the shadow of the disk.Comment: Accepted in ApJ (12 pages long in emulateapj format
Dynamic Failure in Amorphous Solids via a Cavitation Instability
The understanding of dynamic failure in amorphous materials via the
propagation of free boundaries like cracks and voids must go beyond elasticity
theory, since plasticity intervenes in a crucial and poorly understood manner
near the moving free boundary. In this Letter we focus on failure via a
cavitation instability in a radially-symmetric stressed material, set up the
free boundary dynamics taking both elasticity and visco-plasticity into
account, using the recently proposed athermal Shear Transformation Zone theory.
We demonstrate the existence (in amorphous systems) of fast cavitation modes
accompanied by extensive plastic deformations and discuss the revealed physics.Comment: 4 pages, 4 figure
A Parallax Distance to the Microquasar GRS 1915+105 and a Revised Estimate of its Black Hole Mass
Using the Very Long Baseline Array, we have measured a trigonometric parallax
for the micro quasar GRS 1915+105, which contains a black hole and a K-giant
companion. This yields a direct distance estimate of 8.6 (+2.0,-1.6) kpc and a
revised estimate for the mass of the black hole of 12.4 (+2.0,-1.8) Msun. GRS
1915+105 is at about the same distance as some HII regions and water masers
associated with high-mass star formation in the Sagittarius spiral arm of the
Galaxy. The absolute proper motion of GRS 1915+105 is -3.19 +/- 0.03 mas/y and
-6.24 +/- 0.05 mas/y toward the east and north, respectively, which corresponds
to a modest peculiar speed of 22 +/-24 km/s at the parallax distance,
suggesting that the binary did not receive a large velocity kick when the black
hole formed. On one observational epoch, GRS 1915+105 displayed superluminal
motion along the direction of its approaching jet. Considering previous
observations of jet motions, the jet in GRS 1915+105 can be modeled with a jet
inclination to the line of sight of 60 +/- 5 deg and a variable flow speed
between 0.65c and 0.81c, which possibly indicates deceleration of the jet at
distances from the black hole >2000 AU. Finally, using our measurements of
distance and estimates of black hole mass and inclination, we provisionally
confirm our earlier result that the black hole is spinning very rapidly.Comment: 20 pages; 2 tables; 6 figure
Physics of brain dynamics: Fokker-Planck analysis reveals changes in EEG delta-theta interactions in anaesthesia
We use drift and diffusion coefficients to reveal interactions between different oscillatory processes underlying a complex signal and apply the method to EEG delta and theta frequencies in the brain. By analysis of data recorded from rats during anaesthesia, we consider the stability and basins of attraction of fixed points in the phase portrait of the deterministic part of the retrieved stochastic process. We show that different classes of dynamics are associated with deep and light anaesthesia, and we demonstrate that the predominant directionality of the interaction is such that theta drives delt
Three-dimensional molecular dynamics simulations of void coalescence during dynamic fracture of ductile metals
Void coalescence and interaction in dynamic fracture of ductile metals have
been investigated using three-dimensional strain-controlled multi-million atom
molecular dynamics simulations of copper. The correlated growth of two voids
during the coalescence process leading to fracture is investigated, both in
terms of its onset and the ensuing dynamical interactions. Void interactions
are quantified through the rate of reduction of the distance between the voids,
through the correlated directional growth of the voids, and through correlated
shape evolution of the voids. The critical inter-void ligament distance marking
the onset of coalescence is shown to be approximately one void radius based on
the quantification measurements used, independent of the initial separation
distance between the voids and the strain-rate of the expansion of the system.
The interaction of the voids is not reflected in the volumetric asymptotic
growth rate of the voids, as demonstrated here. Finally, the practice of using
a single void and periodic boundary conditions to study coalescence is examined
critically and shown to produce results markedly different than the coalescence
of a pair of isolated voids.Comment: Accepted for publication in Physical Review
Dissipation of Quasiclassical Turbulence in Superfluid He
We compare the decay of turbulence in superfluid He produced by a moving
grid to the decay of turbulence created by either impulsive spin-down to rest
or by intense ion injection. In all cases the vortex line density decays at
late time as . At temperatures above 0.8 K, all methods
result in the same rate of decay. Below 0.8 K, the spin-down turbulence
maintains initial rotation and decays slower than grid turbulence and ion-jet
turbulence. This may be due to a decoupling of the large-scale superfluid flow
from the normal component at low temperatures, which changes its effective
boundary condition from no-slip to slip.Comment: Main article: 5 pages, 3 figures. Supplemental material: 4 pages, 3
figures. Accepted for publication in Physical Review Letter
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