7,995 research outputs found
Evolution of Massive Haloes in non-Gaussian Scenarios
We have performed high-resolution cosmological N-body simulations of a
concordance LCDM model to study the evolution of virialized, dark matter haloes
in the presence of primordial non-Gaussianity. Following a standard procedure,
departures from Gaussianity are modeled through a quadratic Gaussian term in
the primordial gravitational potential, characterized by a dimensionless
non-linearity strength parameter f_NL. We find that the halo mass function and
its redshift evolution closely follow the analytic predictions of Matarrese et
al.(2000). The existence of precise analytic predictions makes the observation
of rare, massive objects at large redshift an even more attractive test to
detect primordial non-Gaussian features in the large scale structure of the
universe.Comment: 7 pages,3 figures, submitted to MNRA
EPR entanglement strategies in two-well BEC
Criteria suitable for measuring entanglement between two different potential
wells in a Bose- Einstein condensation (BEC) are evaluated. We show how to
generate the required entanglement, utilizing either an adiabatic two-mode or
dynamic four-mode interaction strategy, with techniques that take advantage of
s-wave scattering interactions to provide the nonlinear coupling. The dynamic
entanglement method results in an entanglement signature with spatially
separated detectors, as in the Einstein-Podolsky-Rosen (EPR) paradox.Comment: 4 pages, 4 figure
Variable iron-line emission near the black hole of Markarian 766
We investigate the link between ionised Fe X-ray line emission and continuum
emission in the bright nearby AGN, Mrk 766. A new long (433 ks) XMM-Newton
observation is analysed, together with archival data from 2000 and 2001. The
contribution from ionised line emission is measured and its time variations on
short (5-20 ks) timescales are correlated with the continuum emission. The
ionised line flux is found to be highly variable and to be strongly correlated
with the continuum flux, demonstrating an origin for the ionised line emission
that is co-located with the continuum emission. Most likely the emission is
ionised reflection from the accretion disc within a few A.U. of the central
black hole, and its detection marks the first time that such an origin has been
identified other than by fitting to spectral line profiles. Future observations
may be able to measure a time lag and hence achieve reverberation mapping of
AGN at X-ray energies.Comment: Accepted for publication, Astronomy and Astrophysics letter
Rapid X-ray Variability of Seyfert 1 Galaxies
The rapid and seemingly random fluctuations in X-ray luminosity of Seyfert
galaxies provided early support for the standard model in which Seyferts are
powered by a supermassive black hole fed from an accretion disc. However, since
EXOSAT there has been little opportunity to advance our understanding of the
most rapid X-ray variability. Observations with XMM-Newton have changed this.
We discuss some recent results obtained from XMM-Newton observations of Seyfert
1 galaxies. Particular attention will be given to the remarkable similarity
found between the timing properties of Seyferts and black hole X-ray binaries,
including the power spectrum and the cross spectrum (time delays and
coherence), and their implications for the physical processes at work in
Seyferts.Comment: To appear in From X-ray Binaries to Quasars: Black Hole Accretion on
All Mass Scales, ed. T. J. Maccarone, R. P. Fender, and L. C. Ho (Dordrecht:
Kluwer
Binary evolution with LOFT
This is a White Paper in support of the mission concept of the Large
Observatory for X-ray Timing (LOFT), proposed as a medium-sized ESA mission. We
discuss the potential of LOFT for the study of very faint X-ray binaries,
orbital period distribution of black hole X-ray binaries and neutron star spin
up. For a summary, we refer to the paper.Comment: White Paper in Support of the Mission Concept of the Large
Observatory for X-ray Timing. (v2 few typos corrected
On the Correlation of Torque and Luminosity in GX 1+4
Over five years of daily hard X-ray (>20 keV) monitoring of the 2-min
accretion-powered pulsar GX 1+4 with the Compton Gamma Ray Observatory/BATSE
large-area detectors has found nearly continuous rapid spin-down, interrupted
by a bright 200-d spin-up episode. During spin-down, the torque becomes more
negative as the luminosity increases (assuming that the 20-60 keV pulsed flux
traces bolometric luminosity), the opposite of what is predicted by standard
accretion torque theory. No changes in the shape of the 20-100 keV pulsed
energy spectrum were detected, so that a very drastic change in the spectrum
below 20 keV or the pulsed fraction would be required to make the 20-60 keV
pulsed flux a poor luminosity tracer. These are the first observations which
flatly contradict standard magnetic disk accretion theory, and they may have
important implications for understanding the spin evolution of X-ray binaries,
cataclysmic variables, and protostars. We briefly discuss the possibility that
GX 1+4 may be accreting from a retrograde disk during spin-down, as previously
suggested.Comment: 10 pages including 3 PS figures. To appear in ApJ Letter
The model constraints from the observed trends for the quasi-periodic oscillation in RE J1034+396
We analyze the time variability of the X-ray emission of RE J1034+396 -- an
active galactic nucleus with the first firm detection of a quasi-periodic
oscillations (QPO). Based on the results of a wavelet analysis, we find a drift
in the QPO central frequency. The change in the QPO frequency correlates with
the change in the X-ray flux with a short time delay. The data specifically
suggest a linear dependence between the QPO period and the flux, and this gives
important constraints on the QPO models. In particular, it excludes explanation
in terms of the orbiting hot spot model close to a black hole. Linear
structures such as shocks, spiral waves, or very distant flares are favored.Comment: Astronomy & Astrophysics, in pres
Non-extremal Black Holes, Harmonic Functions, and Attractor Equations
We present a method which allows to deform extremal black hole solutions into
non-extremal solutions, for a large class of supersymmetric and
non-supersymmetric Einstein-Vector-Scalar type theories. The deformation is
shown to be largely independent of the details of the matter sector. While the
line element is dressed with an additional harmonic function, the attractor
equations for the scalars remain unmodified in suitable coordinates, and the
values of the scalar fields on the outer and inner horizon are obtained from
their fixed point values by making specific substitutions for the charges. For
a subclass of models, which includes the five-dimensional STU-model, we find
explicit solutions.Comment: 33 page
Fast Spectral Variability from Cygnus X-1
We have developed an algorithm that, starting from the observed properties of
the X-ray spectrum and fast variability of an X-ray binary allows the
production of synthetic data reproducing observables such as power density
spectra and time lags, as well as their energy dependence. This allows to
reconstruct the variability of parameters of the energy spectrum and to reduce
substantially the effects of Poisson noise, allowing to study fast spectral
variations. We have applied the algorithm to Rossi X-ray Timing Explorer data
of the black-hole binary Cygnus X-1, fitting the energy spectrum with a
simplified power law model. We recovered the distribution of the power law
spectral indices on time-scales as low as 62 ms as being limited between 1.6
and 1.8. The index is positively correlated with the flux even on such
time-scales.Comment: 14 pages, 19 figures, accepted by MNRA
Structure and evolution of Cenozoic arc magmatism on the Antarctic Peninsula: a high resolution aeromagnetic perspective
The Antarctic Peninsula (AP) consists of a long lived and uniquely well preserved magmatic arc system. The broad tectonic structure of the AP arc is well understood. However, magmatic processes occurring along the arc are only constrained by regional geophysical and relatively sparse geological data. Key questions remain about the timing, volume, and structural controls on magma emplacement. We present new high resolution aeromagnetic data across Adelaide Island, on the western margin of the AP revealing the complex structure of the AP arc/forearc boundary. Using digital enhancement, 2-D modelling and 3-D inversion we constrain the form of the magnetic sources at the arc/forearc boundary. Our interpretation of these magnetic data, guided by geological evidence and new zircon U-Pb dating, suggests significant Palaeogene to Neogene magmatism formed ∼25 per cent of the upper crust in this region (∼7500 km3). Significant structural control on Neogene magma emplacement along the arc/forearc boundary is also revealed. We hypothesize that this Neogene magmatism reflects mantle return flow through a slab window generated by Late Palaeogene cessation of subduction south of Adelaide Island. This mantle process may have affected the final stages of arc magmatism along the AP margin
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