38 research outputs found
Integrability breakdown in longitudinaly trapped, one-dimensional bosonic gases
A system of identical bosons with short-range (contact) interactions is
studied. Their motion is confined to one dimension by a tight lateral trapping
potential and, additionally, subject to a weak harmonic confinement in the
longitudinal direction. Finite delay time associated with penetration of
quantum particles through each other in the course of a pairwise
one-dimensional collision in the presence of the longitudinal potential makes
the system non-integrable and, hence, provides a mechanism for relaxation to
thermal equilibrium. To analyse this effect quantitatively in the limit of a
non-degenerate gas, we develop a system of kinetic equations and solve it for
small-amplitude monopole oscillations of the gas. The obtained damping rate is
long enough to be neglected in a realistic cold-atom experiment, and therefore
longitudinal trapping does not hinder integrable dynamics of atomic gases in
the 1D regime
Giant Flare in SGR 1806-20 and Its Compton Reflection from the Moon
We analyze the data obtained when the Konus-Wind gamma-ray spectrometer
detected a giant flare in SGR 1806-20 on December 27, 2004. The flare is
similar in appearance to the two known flares in SGR 0526-66 and SGR 1900+14
while exceeding them significantly in intensity. The enormous X-ray and
gamma-ray flux in the narrow initial pulse of the flare leads to almost
instantaneous deep saturation of the gamma-ray detectors, ruling out the
possibility of directly measuring the intensity, time profile, and energy
spectrum of the initial pulse. In this situation, the detection of an
attenuated signal of Compton back-scattering of the initial pulse emission by
the Moon with the Helicon gamma-ray spectrometer onboard the Coronas-F
satellite was an extremely favorable circumstance. Analysis of this signal has
yielded the most reliable temporal, energy, and spectral characteristics of the
pulse. The temporal and spectral characteristics of the pulsating flare tail
have been determined from Konus-Wind data. Its soft spectra have been found to
contain also a hard power-law component extending to 10 MeV. A weak afterglow
of SGR 1806-20 decaying over several hours is traceable up to 1 MeV. We also
consider the overall picture of activity of SGR 1806-20 in the emission of
recurrent bursts before and after the giant flare.Comment: 29 pages including 18 figures; to appear in Astronomy Letters, 2007,
33, p 1-1
Unveiling Soft Gamma-Ray Repeaters with INTEGRAL
Thanks to INTEGRAL's long exposures of the Galactic Plane, the two brightest
Soft Gamma-Ray Repeaters, SGR 1806-20 and SGR 1900+14, have been monitored and
studied in detail for the first time at hard-X/soft gamma rays.
This has produced a wealth of new scientific results, which we will review
here. Since SGR 1806-20 was particularly active during the last two years, more
than 300 short bursts have been observed with INTEGRAL. and their
characteristics have been studied with unprecedented sensitivity in the 15-200
keV range. A hardness-intensity anticorrelation within the bursts has been
discovered and the overall Number-Intensity distribution of the bursts has been
determined. In addition, a particularly active state, during which ~100 bursts
were emitted in ~10 minutes, has been observed on October 5 2004, indicating
that the source activity was rapidly increasing. This eventually led to the
Giant Flare of December 27th 2004, for which a possible soft gamma-ray (>80
keV) early afterglow has been detected.
The deep observations allowed us to discover the persistent emission in hard
X-rays (20-150 keV) from 1806-20 and 1900+14, the latter being in a quiescent
state, and to directly compare the spectral characteristics of all Magnetars
(two SGRs and three Anomalous X-ray Pulsars) detected with INTEGRAL.Comment: 8 pages, 7 figures, Presented at the conference "Isolated Neutron
Stars: from the Surface to the Interior", London, UK, 24-28 April 200
About the measurements of the hard X-ray background
We analyze uncertainties in the cosmic X-ray background measurements
performed by the INTEGRAL observatory. We find that the most important effect
limiting the accuracy of the measurements is related to the intrinsic
background variation in detectors. Taking into account all of the uncertainties
arising during the measurements we conclude that the X-ray background intensity
obtained in the INTEGRAL observations is compatible with the historic X-ray
background observations performed by the HEAO-1 satellite.Comment: 20 pages, 4 figures, accepted for publication in Astrophysics and
Space Scienc
United classification of cosmic gamma-ray bursts and their counterparts
United classification of gamma-ray bursts and their counterparts is
established on the basis of measured characteristics: photon energy E and
emission duration T. The founded interrelation between the mentioned
characteristics of events consists in that, as the energy increases, the
duration decreases (and vice versa). The given interrelation reflects the
nature of the phenomenon and forms the E-T diagram, which represents a natural
classification of all observed events in the energy range from 10E9 to 10E-6 eV
and in the corresponding interval of durations from about 10E-2 up to 10E8 s.
The proposed classification results in the consequences, which are principal
for the theory and practical study of the phenomenon.Comment: Keywords Gamma rays: burst
Newborn Magnetars as sources of Gravitational Radiation: constraints from High Energy observations of Magnetar Candidates
Soft Gamma Repeaters and the Anomalous X-ray Pulsars are believed to contain
slowly spinning "magnetars". The enormous energy liberated in the 2004 Dece 27
giant flare from SGR 1806-20, together with the likely recurrence time of such
events, points to an internal magnetic field strength ~ 10^{16} G. Such strong
fields are expected to be generated by a coherent alpha-Omega dynamo in the
early seconds after the Neutron Star formation, if its spin period is of a few
milliseconds at most. A substantial deformation of the NS is caused by such
fields and a newborn millisecond-spinning magnetar would thus radiate for a few
days a strong gravitational wave signal. Such a signal may be detected with
Advanced LIGO-class detectors up to the distance of the Virgo cluster, where ~
1 magnetar per year are expected to form. Recent X-ray observations reveal that
SNRs around magnetar candidates do not show evidence for a larger energy
content than standard SNRs (Vink & Kuiper 2006). This is at variance with what
would be expected if the spin energy of the young, millisecond NS were radiated
away as electromagnetic radiation andd/or relativistic particle winds and,
thus, transferred quickly to the expanding gas shell. We show here that these
recent findings can be reconciled with the idea of magnetars being formed with
fast spins, if most of their initial spin energy is radiated thorugh GWs. In
particular, we find that this occurs for essentially the same parameter range
that would make such objects detectable by Advanced LIGO-class detectors up to
the Virgo Cluster.Comment: Proceedings of the Conference "Isolated Neutron stars: from the
interior to the surface", Eds. D. Page, R. Turolla, S. Zan
Magnetic Reconnection in Extreme Astrophysical Environments
Magnetic reconnection is a basic plasma process of dramatic rearrangement of
magnetic topology, often leading to a violent release of magnetic energy. It is
important in magnetic fusion and in space and solar physics --- areas that have
so far provided the context for most of reconnection research. Importantly,
these environments consist just of electrons and ions and the dissipated energy
always stays with the plasma. In contrast, in this paper I introduce a new
direction of research, motivated by several important problems in high-energy
astrophysics --- reconnection in high energy density (HED) radiative plasmas,
where radiation pressure and radiative cooling become dominant factors in the
pressure and energy balance. I identify the key processes distinguishing HED
reconnection: special-relativistic effects; radiative effects (radiative
cooling, radiation pressure, and Compton resistivity); and, at the most extreme
end, QED effects, including pair creation. I then discuss the main
astrophysical applications --- situations with magnetar-strength fields
(exceeding the quantum critical field of about 4 x 10^13 G): giant SGR flares
and magnetically-powered central engines and jets of GRBs. Here, magnetic
energy density is so high that its dissipation heats the plasma to MeV
temperatures. Electron-positron pairs are then copiously produced, making the
reconnection layer highly collisional and dressing it in a thick pair coat that
traps radiation. The pressure is dominated by radiation and pairs. Yet,
radiation diffusion across the layer may be faster than the global Alfv\'en
transit time; then, radiative cooling governs the thermodynamics and
reconnection becomes a radiative transfer problem, greatly affected by the
ultra-strong magnetic field. This overall picture is very different from our
traditional picture of reconnection and thus represents a new frontier in
reconnection research.Comment: Accepted to Space Science Reviews (special issue on magnetic
reconnection). Article is based on an invited review talk at the
Yosemite-2010 Workshop on Magnetic Reconnection (Yosemite NP, CA, USA;
February 8-12, 2010). 30 pages, no figure
Status of the GAMMA-400 Project
The preliminary design of the new space gamma-ray telescope GAMMA-400 for the
energy range 100 MeV - 3 TeV is presented. The angular resolution of the
instrument, 1-2{\deg} at E{\gamma} ~100 MeV and ~0.01^{\circ} at E{\gamma} >
100 GeV, its energy resolution ~1% at E{\gamma} > 100 GeV, and the proton
rejection factor ~10E6 are optimized to address a broad range of science
topics, such as search for signatures of dark matter, studies of Galactic and
extragalactic gamma-ray sources, Galactic and extragalactic diffuse emission,
gamma-ray bursts, as well as high-precision measurements of spectra of
cosmic-ray electrons, positrons, and nuclei.Comment: 6 pages, 1 figure, 1 table, submitted to Advances in Space Researc
Ioffe Institute GRB experiments: past, present and future
The short review of GRB studies performed for many years by Ioffe Institute is presented.
An important breakthrough in GRB studies became possible owing to four Konus experiments
carried out by the Ioffe Institute onboard the Venera 11 to 14 interplanetary missions
from 1978 to 1983. The joint Russian-American Konus-Wind experiment, which has already
been operating for more than 18 years, provides important and often unique data regarding
GRB characteristics in 20 keV â 15 MeV energy range. These investigations were
complemented by several Konus and Helicon experiments onboard Russian near-Earth
spacecraft. A short description of future Konus-UF and Konus-M experiments are also
given