1,297 research outputs found
Comparison of time/phase lags in the hard state and plateau state of GRS 1915+105
We investigate the complex behavior of energy- and frequency-dependent
time/phase lags in the plateau state and the radio-quiet hard state of GRS
1915+105. In our timing analysis, we find that when the source is faint in the
radio, QPOs are observed above 2 Hz and typically exhibit soft lags (soft
photons lag hard photons), whereas QPOs in the radio-bright plateau state are
found below 2.2 Hz and consistently show hard lags. The phase lag at the QPO
frequency is strongly anti-correlated with the QPO frequency, changing sign at
2.2 Hz. However, the phase lag at the frequency of the first harmonic is
positive and nearly independent of frequency at at ~0.172 rad, regardless of
the radio emission. The lag-energy dependence at the first harmonic is also
independent of radio flux. However, the lags at the QPO frequency are negative
at all energies during the radio-quiet state, but lags at the QPO frequency
during the plateau state are positive at all energies and show a
'reflection-type' evolution of the lag-energy spectra with respect to the
radio-quiet state. The lag-energy dependence is roughly logarithmic, but there
is some evidence for a break around 4-6 keV. Finally, the Fourier
frequency-dependent phase lag spectra are fairly flat during the plateau state,
but increase from negative to positive during the radio-quiet state. We discuss
the implications of our results in the light of some generic models.Comment: 9 pages, 7 figures, accepted for publication in Ap
The effect of spin-orbit interaction on entanglement of two-qubit Heisenberg XYZ systems in an inhomogeneous magnetic field
The role of spin-orbit interaction on the ground state and thermal
entanglement of a Heisenberg XYZ two-qubit system in the presence of an
inhomogeneous magnetic field is investigated. For a certain value of spin-orbit
parameter , the ground state entanglement tends to vanish suddenly and when
crosses its critical value , the entanglement undergoes a revival. The
maximum value of the entanglement occurs in the revival region. In finite
temperatures there are revival regions in plane. In these regions,
entanglement first increases with increasing temperature and then decreases and
ultimately vanishes for temperatures above a critical value. This critical
temperature is an increasing function of , thus the nonzero entanglement can
exist for larger temperatures. In addition, the amount of entanglement in the
revival region depends on the spin-orbit parameter. Also, the entanglement
teleportation via the quantum channel constructed by the above system is
investigated and finally the influence of the spin-orbit interaction on the
fidelity of teleportation and entanglement of replica state is studied.Comment: Two columns, 9 pages, 8 Fig
Ubiquitous equatorial accretion disc winds in black hole soft states
High resolution spectra of Galactic Black Holes (GBH) reveal the presence of
highly ionised absorbers. In one GBH, accreting close to the Eddington limit
for more than a decade, a powerful accretion disc wind is observed to be
present in softer X-ray states and it has been suggested that it can carry away
enough mass and energy to quench the radio jet. Here we report that these
winds, which may have mass outflow rates of the order of the inner accretion
rate or higher, are an ubiquitous component of the jet-free soft states of all
GBH. We furthermore demonstrate that these winds have an equatorial geometry
with opening angles of few tens of degrees, and so are only observed in sources
in which the disc is inclined at a large angle to the line of sight. The
decrease in Fe XXV / Fe XXVI line ratio with Compton temperature, observed in
the soft state, suggests a link between higher wind ionisation and harder
spectral shapes. Although the physical interaction between the wind, accretion
flow and jet is still not fully understood, the mass flux and power of these
winds, and their presence ubiquitously during the soft X-ray states suggests
they are fundamental components of the accretion phenomenon.Comment: Accepted for publication in MNRAS Letter
Numerical stability of a new conformal-traceless 3+1 formulation of the Einstein equation
There is strong evidence indicating that the particular form used to recast
the Einstein equation as a 3+1 set of evolution equations has a fundamental
impact on the stability properties of numerical evolutions involving black
holes and/or neutron stars. Presently, the longest lived evolutions have been
obtained using a parametrized hyperbolic system developed by Kidder, Scheel and
Teukolsky or a conformal-traceless system introduced by Baumgarte, Shapiro,
Shibata and Nakamura. We present a new conformal-traceless system. While this
new system has some elements in common with the
Baumgarte-Shapiro-Shibata-Nakamura system, it differs in both the type of
conformal transformations and how the non-linear terms involving the extrinsic
curvature are handled. We show results from 3D numerical evolutions of a
single, non-rotating black hole in which we demonstrate that this new system
yields a significant improvement in the life-time of the simulations.Comment: 7 pages, 2 figure
Relativistic MHD with Adaptive Mesh Refinement
This paper presents a new computer code to solve the general relativistic
magnetohydrodynamics (GRMHD) equations using distributed parallel adaptive mesh
refinement (AMR). The fluid equations are solved using a finite difference
Convex ENO method (CENO) in 3+1 dimensions, and the AMR is Berger-Oliger.
Hyperbolic divergence cleaning is used to control the
constraint. We present results from three flat space tests, and examine the
accretion of a fluid onto a Schwarzschild black hole, reproducing the Michel
solution. The AMR simulations substantially improve performance while
reproducing the resolution equivalent unigrid simulation results. Finally, we
discuss strong scaling results for parallel unigrid and AMR runs.Comment: 24 pages, 14 figures, 3 table
Evolutions of Magnetized and Rotating Neutron Stars
We study the evolution of magnetized and rigidly rotating neutron stars
within a fully general relativistic implementation of ideal
magnetohydrodynamics with no assumed symmetries in three spatial dimensions.
The stars are modeled as rotating, magnetized polytropic stars and we examine
diverse scenarios to study their dynamics and stability properties. In
particular we concentrate on the stability of the stars and possible critical
behavior. In addition to their intrinsic physical significance, we use these
evolutions as further tests of our implementation which incorporates new
developments to handle magnetized systems.Comment: 12 pages, 8 figure
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