1,284 research outputs found
The Physics of Disk Winds, Jets,and X-ray Variability in GRS 1915+105
We present new insights about accretion and ejection physics based on joint
RXTE/Chandra HETGS studies of rapid X-ray variability in GRS 1915+105. For the
first time, with fast phase-resolved spectroscopy of the rho state, we are able
to show that changes in the broadband X-ray spectrum (RXTE) on timescales of
seconds are associated with measurable changes in absorption lines (Chandra
HETGS) from the accretion disk wind. Additionally, we make a direct detection
of material evaporating from the radiation-pressure-dominated inner disk. Our
X-ray data thus reveal the black hole as it ejects a portion of the inner
accretion flow and then drives a wind from the outer disk, all in a bizarre
cycle that lasts fewer than 60 seconds but can repeat for weeks. We find that
the accretion disk wind may be sufficiently massive to play an active role in
GRS 1915+105, not only in quenching the jet on long timescales, but also in
possibly producing or facilitating transitions between classes of X-ray
variability.Comment: 3 pages, 1 Figure. Proceedings of IAU Symposium 275 (Jets at all
Scales), Buenos Aires, 13-17.09.2010; eds. G. Romero, R. Sunyaev, T. Bellon
Phase Variation in the Pulse Profile of SMC X-1
We present the results of timing and spectral analysis of X-ray high state
observations of the high-mass X-ray pulsar SMC X-1 with Chandra, XMM-Newton,
and ROSAT, taken between 1991 and 2001. The source has L_X ~ 3-5 x 10^38
ergs/s, and the spectra can be modeled as a power law plus blackbody with kT_BB
\~ 0.18 keV and reprocessed emission radius R_BB ~ 2 x 10^8 cm, assuming a
distance of 60 kpc to the source. Energy-resolved pulse profiles show several
distinct forms, more than half of which include a second pulse in the soft
profile, previously documented only in hard energies. We also detect
significant variation in the phase shift between hard and soft pulses, as has
recently been reported in Her X-1. We suggest an explanation for the observed
characteristics of the soft pulses in terms of precession of the accretion
disk.Comment: 4 pages, 4 figures, accepted for publication in ApJL; v2 minor
corrections, as will appear in ApJ
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
The Physics of the 'Heartbeat' State of GRS 1915+105
We present the first detailed phase-resolved spectral analysis of a joint
Chandra High Energy Transmission Grating Spectrometer and Rossi X-ray Timing
Explorer observation of the rho variability class in the microquasar GRS
1915+105. The rho cycle displays a high-amplitude, double-peaked flare that
recurs roughly every 50 s, and is sometimes referred to as the "heartbeat"
oscillation. The spectral and timing properties of the oscillation are
consistent with the radiation pressure instability and the evolution of a local
Eddington limit in the inner disk. We exploit strong variations in the X-ray
continuum, iron emission lines, and the accretion disk wind to probe the
accretion geometry over nearly six orders of magnitude in distance from the
black hole. At small scales (1-10 R_g), we detect a burst of bremsstrahlung
emission that appears to occur when a portion of the inner accretion disk
evaporates due to radiation pressure. Jet activity, as inferred from the
appearance of a short X-ray hard state, seems to be limited to times near
minimum luminosity, with a duty cycle of ~10%. On larger scales (1e5-1e6 R_g)
we use detailed photoionization arguments to track the relationship between the
fast X-ray variability and the accretion disk wind. For the first time, we are
able to show that changes in the broadband X-ray spectrum produce changes in
the structure and density of the accretion disk wind on timescales as short as
5 seconds. These results clearly establish a causal link between the X-ray
oscillations and the disk wind and therefore support the existence of a
disk-jet-wind connection. Furthermore, our analysis shows that the mass loss
rate in the wind may be sufficient to cause long-term oscillations in the
accretion rate, leading to state transitions in GRS 1915+105.Comment: Accepted to ApJ. 22 pages, 14 figures, uses emulateap
Entanglement without nonlocality
We consider the characterization of entanglement from the perspective of a
Heisenberg formalism. We derive an original two-party generalized separability
criteria, and from this describe a novel physical understanding of
entanglement. We find that entanglement may be considered as fundamentally a
local effect, and therefore as a separable computational resource from
nonlocality. We show how entanglement differs from correlation physically, and
explore the implications of this new conception of entanglement for the notion
of classicality. We find that this understanding of entanglement extends
naturally to multipartite cases.Comment: 9 pages. Expanded introduction and sections on physical entanglement
and localit
Boosting jet power in black hole spacetimes
The extraction of rotational energy from a spinning black hole via the
Blandford-Znajek mechanism has long been understood as an important component
in models to explain energetic jets from compact astrophysical sources. Here we
show more generally that the kinetic energy of the black hole, both rotational
and translational, can be tapped, thereby producing even more luminous jets
powered by the interaction of the black hole with its surrounding plasma. We
study the resulting Poynting jet that arises from single boosted black holes
and binary black hole systems. In the latter case, we find that increasing the
orbital angular momenta of the system and/or the spins of the individual black
holes results in an enhanced Poynting flux.Comment: 7 pages, 5 figure
Critical Phenomena in Neutron Stars I: Linearly Unstable Nonrotating Models
We consider the evolution in full general relativity of a family of linearly
unstable isolated spherical neutron stars under the effects of very small,
perturbations as induced by the truncation error. Using a simple ideal-fluid
equation of state we find that this system exhibits a type-I critical
behaviour, thus confirming the conclusions reached by Liebling et al. [1] for
rotating magnetized stars. Exploiting the relative simplicity of our system, we
are able carry out a more in-depth study providing solid evidences of the
criticality of this phenomenon and also to give a simple interpretation of the
putative critical solution as a spherical solution with the unstable mode being
the fundamental F-mode. Hence for any choice of the polytropic constant, the
critical solution will distinguish the set of subcritical models migrating to
the stable branch of the models of equilibrium from the set of subcritical
models collapsing to a black hole. Finally, we study how the dynamics changes
when the numerically perturbation is replaced by a finite-size, resolution
independent velocity perturbation and show that in such cases a nearly-critical
solution can be changed into either a sub or supercritical. The work reported
here also lays the basis for the analysis carried in a companion paper, where
the critical behaviour in the the head-on collision of two neutron stars is
instead considered [2].Comment: 15 pages, 9 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
Continuous Variable Quantum State Sharing via Quantum Disentanglement
Quantum state sharing is a protocol where perfect reconstruction of quantum
states is achieved with incomplete or partial information in a multi-partite
quantum networks. Quantum state sharing allows for secure communication in a
quantum network where partial information is lost or acquired by malicious
parties. This protocol utilizes entanglement for the secret state distribution,
and a class of "quantum disentangling" protocols for the state reconstruction.
We demonstrate a quantum state sharing protocol in which a tripartite entangled
state is used to encode and distribute a secret state to three players. Any two
of these players can collaborate to reconstruct the secret state, whilst
individual players obtain no information. We investigate a number of quantum
disentangling processes and experimentally demonstrate quantum state
reconstruction using two of these protocols. We experimentally measure a
fidelity, averaged over all reconstruction permutations, of F = 0.73. A result
achievable only by using quantum resources.Comment: Published, Phys. Rev. A 71, 033814 (2005) (7 figures, 11 pages
Suzaku X-ray Spectra and Pulse Profile Variations during the Superorbital Cycle of LMC X-4
We present results from spectral and temporal analyses of Suzaku and RXTE
observations of the high mass X-ray binary LMC X-4. Using the full 13 years of
available RXTE/ASM data, we apply the ANOVA and Lomb normalized Periodogram
methods to obtain an improved superorbital period measurement of 30.32 +/- 0.04
days. The phase-averaged X-ray spectra from Suzaku observations during the high
state of the superorbital period can be modeled in the 0.6--50 keV band as the
combination of a power-law with Gamma ~ 0.6 and a high-energy cutoff at ~ 25
keV, a blackbody with kT_BB ~ 0.18 keV, and emission lines from Fe K_alpha, O
VIII, and Ne IX (X Lyalpha). Assuming a distance of 50 kpc, The source has
luminosity L_X ~ 3 x 10^38 ergs s^-1 in the 2--50 keV band, and the luminosity
of the soft (blackbody) component is L_BB ~ 1.5 x 10^37 ergs s^-1. The energy
resolved pulse profiles show single-peaked soft (0.5-1 keV) and hard (6-10 keV)
pulses but a more complex pattern of medium (2-10 keV) pulses;
cross-correlation of the hard with the soft pulses shows a phase shift that
varies between observations. We interpret these results in terms of a picture
in which a precessing disk reprocesses the hard X-rays and produces the
observed soft spectral component, as has been suggested for the similar sources
Her X-1 and SMC X-1.Comment: 13 emulateapj pages, 11 figures, 4 tables; accepted for publication
in Ap
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