5,331 research outputs found
Quasiperiodic surface Maryland models on quantum graphs
We study quantum graphs corresponding to isotropic lattices with
quasiperiodic coupling constants given by the same expressions as the
coefficients of the discrete surface Maryland model. The absolutely continuous
and the pure point spectra are described. It is shown that the transition
between them is governed by the Hill operator corresponding to the edge
potential.Comment: 12 page
Observations of the X-ray Afterglows of GRB011211 and GRB001025 by XMM-Newton
We present the XMM-Newton observations of X-ray afterglows of the gamma-ray
bursts GRB 011211 and GRB 001025. For GRB 011211 XMM detected fading X-ray
object with an average flux in 0.2-10 keV declining from 2.7
erg cm s during the first 5 ks of 27-ks observation to
1.0 erg cm s toward the end of the observation.
The spectrum of the afterglow can be fit to a power law with
alpha=2.160.03 modified for the Galactic absorption. No significant
evolution of spectral parameters has been detected during the observation.
Similar X-ray spectrum with alpha=2.010.09 has been observed by the XMM
from the GRB 001025. The non-detection of any extra absorption in these spectra
above the Galactic value is an interesting fact and may impose restrictions to
the favorable GRB models involving burst origin in star-forming regions.
Finally we discuss soft X-ray lines from GRB 011211 reported by Reeves et
al.(2002) and conclude that there is no definitive evidence for the presense of
these lines in the spectrum.Comment: submitted to ApJL (7 pages, 4 figures, 2 tables, emulateapj.sty
In Situ Formation and Dynamical Evolution of Hot Jupiter Systems
Hot Jupiters, giant extrasolar planets with orbital periods shorter than ~10
days, have long been thought to form at large radial distances, only to
subsequently experience long-range inward migration. Here, we propose that in
contrast with this picture, a substantial fraction of the hot Jupiter
population formed in situ via the core accretion process. We show that under
conditions appropriate to the inner regions of protoplanetary disks, rapid gas
accretion can be initiated by Super-Earth type planets, comprising 10-20 Earth
masses of refractory composition material. An in situ formation scenario leads
to testable consequences, including the expectation that hot Jupiters should
frequently be accompanied by additional low-mass planets with periods shorter
than ~100 days. Our calculations further demonstrate that dynamical
interactions during the early stages of planetary systems' lifetimes should
increase the inclinations of such companions, rendering transits rare.
High-precision radial velocity monitoring provides the best prospect for their
detection.Comment: 19 pages, 10 figures, accepted to Ap
Time-resolved broadband Raman spectroscopies; A unified six-wave-mixing representation
Excited-state vibrational dynamics in molecules can be studied by an
electronically off-resonant Raman process induced by a probe pulse with
variable delay with respect to an actinic pulse. We establish the connection
between several variants of the technique that involve either spontaneous or
stimulated Raman detection and different pulse configurations. By using loop
diagrams in the frequency domain we show that all signals can be described as
six wave mixing which depend on the same four point molecular correlation
functions involving two transition dipoles and two polarizabilities and
accompanied by a different gating. Simulations for the stochastic
two-state-jump model illustrate the origin of the absorptive and dispersive
features observed experimentally
Broadband infrared and Raman probes of excited-state vibrational molecular dynamics; Simulation protocols based on loop diagram
Vibrational motions in electronically excited states can be observed by
either time and frequency resolved infrared absorption or by off resonant
stimulated Raman techniques. Multipoint correlation function expressions are
derived for both signals. Three representations for the signal which suggest
different simulation protocols are developed. These are based on the forward
and the backward propagation of the wavefunction, sum over state expansion
using an effective vibration Hamiltonian and a semiclassical treatment of a
bath. We show that the effective temporal () and spectral
() resolution of the techniques is not controlled solely by
experimental knobs but also depends on the system dynamics being probed. The
Fourier uncertainty is never violated
Barotropic thin shells with linear EOS as models of stars and circumstellar shells in general relativity
The spherically symmetric thin shells of the barotropic fluids with the
linear equation of state are considered within the frameworks of general
relativity. We study several aspects of the shells as completely relativistic
models of stars, first of all the neutron stars and white dwarfs, and
circumstellar shells. The exact equations of motion of the shells are obtained.
Also we calculate the parameters of the equilibrium configurations, including
the radii of static shells. Finally, we study the stability of the equilibrium
shells against radial perturbations.Comment: final version; ps-version of figure is available by email request to
[email protected]
RXTE observations of 4U 1630-47 during the peak of its 1998 outburst
We present an analysis of the RXTE observations of 4U 1630-47 during its
outburst of 1998. The light curve and the spectral evolution of the outburst
were distinctly different from the outbursts of the same source in 1996 and in
1999. Special emphasis of our analysis was on the observations taken during the
initial rise of the flux and during the maximum of the outburst. The maximum of
the outburst was divided into three plateaus, with almost constant flux within
each plateau, and fast jumps between them. The spectral and timing parameters
are stable for each individual plateau, but distinctly different between the
plateaus. The variability detected on the first plateau is of special interest.
During these observations the source exhibits quasi-regular modulations with
period of ~10 - 20 s. Our analysis revealed significant differences in spectral
and temporal behavior of the source at high and low fluxes during this period
of time. The source behavior can be generally explained in the framework of the
two-phase model of the accretion flow, involving a hot inner comptonization
region and surrounding optically thick disk. The variability and spectral
evolution of the source were similar to what was observed earlier for other
X-ray Novae. We show that 4U 1630-47 has a variety of properties which are
typical for Galactic black hole binaries, both transient and persistent. We
argue that this system may be an intermediate case between different groups of
black hole candidates.Comment: 14 pages, 12 figures, submitted to MNRA
- âŠ