939 research outputs found
A population of isolated hard X-ray sources near the supernova remnant Kes 69
Recent X-ray observations of the supernova remnant IC443 interacting with
molecular clouds have shown the presence of a new population of hard X-ray
sources related to the remnant itself, which has been interpreted in terms of
fast ejecta fragment propagating inside the dense environment. Prompted by
these studies, we have obtained a deep {\sl XMM-Newton} observation of the
supernova remnant (SNR) Kes 69, which also shows signs of shock-cloud
interaction. We report on the detection of 18 hard X-ray sources in the field
of Kes 69, a significant excess of the expected galactic source population in
the field, spatially correlated with CO emission from the cloud in the remnant
environment. The spectra of 3 of the 18 sources can be described as hard power
laws with photon index <2 plus line emission associated to K-shell transitions.
We discuss the two most promising scenarios for the interpretation of the
sources, namely fast ejecta fragments (as in IC443) and cataclysmic variables.
While most of the observational evidences are consistent with the former
interpretation, we cannot rule out the latter.Comment: 9 pages, 5 figures, A&A in pres
Diffusive Radiation in One-dimensional Langmuir Turbulence
We calculate spectra of radiation produced by a relativistic particle in the
presence of one-dimensional Langmuir turbulence which might be generated by a
streaming instability in the plasma, in particular, in the shock front or at
the shock-shock interactions. The shape of the radiation spectra is shown to
depend sensitively on the angle between the particle velocity and electric
field direction. The radiation spectrum in the case of exactly transverse
particle motion is degenerate and similar to that of spatially uniform Langmuir
oscillations. In case of oblique propagation, the spectrum is more complex, it
consists of a number of power-law regions and may contain a distinct
high-frequency spectral peak. %at \omega=2\omega\pe \gamma^2. The emission
process considered is relevant to various laboratory plasma settings and for
astrophysical objects as gamma-ray bursts and collimated jets.Comment: 4 pages, 1 figure, accepted for Phys. Rev.
Master equation for collective spontaneous emission with quantized atomic motion
We derive a markovian master equation for the internal dynamics of an
ensemble of two-level atoms including all effects related to the quantization
of their motion. Our equation provides a unifying picture of the consequences
of recoil and indistinguishability of atoms beyond the Lamb-Dicke regime on
both their dissipative and conservative dynamics, and applies equally well to
distinguishable and indistinguishable atoms. We give general expressions for
the decay rates and the dipole-dipole shifts for any motional states, and we
find closed-form formulas for a number of relevant states (Gaussian states,
Fock states and thermal states). In particular, we show that dipole-dipole
interactions and cooperative photon emission can be modulated through the
external state of motion.Comment: 16 pages, 7 figures, minor correction
Magnetic fields in cosmic particle acceleration sources
We review here some magnetic phenomena in astrophysical particle accelerators
associated with collisionless shocks in supernova remnants, radio galaxies and
clusters of galaxies. A specific feature is that the accelerated particles can
play an important role in magnetic field evolution in the objects. We discuss a
number of CR-driven, magnetic field amplification processes that are likely to
operate when diffusive shock acceleration (DSA) becomes efficient and
nonlinear. The turbulent magnetic fields produced by these processes determine
the maximum energies of accelerated particles and result in specific features
in the observed photon radiation of the sources. Equally important, magnetic
field amplification by the CR currents and pressure anisotropies may affect the
shocked gas temperatures and compression, both in the shock precursor and in
the downstream flow, if the shock is an efficient CR accelerator. Strong
fluctuations of the magnetic field on scales above the radiation formation
length in the shock vicinity result in intermittent structures observable in
synchrotron emission images. Resonant and non-resonant CR streaming
instabilities in the shock precursor can generate mesoscale magnetic fields
with scale-sizes comparable to supernova remnants and even superbubbles. This
opens the possibility that magnetic fields in the earliest galaxies were
produced by the first generation Population III supernova remnants and by
clustered supernovae in star forming regions.Comment: 30 pages, Space Science Review
Ladders for Wilson Loops Beyond Leading Order
We set up a general scheme to resum ladder diagrams for the quark-anti-quark
potential in N=4 super-Yang-Mills theory, and do explicit calculations at the
next-to-leading order. The results perfectly agree with string theory in
AdS(5)xS(5) when continued to strong coupling, in spite of a potential
order-of-limits problem.Comment: 18 pages, 5 figure
Linear in-plane magnetoconductance and spin susceptibility of a 2D electron gas on a vicinal silicon surface
In this work we have studied the parallel magnetoresistance of a 2DEG near a
vicinal silicon surface. An unusual, linear magnetoconductance is observed in
the fields up to T, which we explain by the effect of spin olarization
on impurity scattering. This linear magnetoresistance shows strong anomalies
near the boundaries of the minigap in the electron spectrum of the vicinal
system.Comment: (accepted to Phys. Rev. B
Thermal and Non-thermal X-Rays from the LMC Super Bubble 30 Dor C
We report on the discovery of thermal and non-thermal X-rays from the shells
of the super bubble (SB) 30 Dor C in the Large Magellanic Cloud (LMC). The
X-ray morphology is a nearly circular shell with a radius of about 40 pc, which
is bright on the northern and western sides. The spectra of the shells are
different from region to region. The southern shell shows clear emission lines,
and is well fitted with a model of a thin-thermal plasma (kT = 0.21keV) in
non-equilibrium ionization (NEI) plus a power-law component. This thermal
plasma is located inside of the H alpha emission, which is the outer edge of
the shell of the SB. The northern and western sides of the SB are dim in H
alpha emission, but are bright in non-thermal (power-law) X-rays with a photon
index of 2.1-2.9. The non-thermal X-ray shell traces the outer boundary of the
radio shell. These features of thin-thermal and non-thermal X-rays are similar
to those of SN 1006, a prototype of synchrotron X-ray shell, but the
non-thermal component of 30 Dor C is about ten-times brighter than that of SN
1006. 30 Dor C is the first candidate of an extragalactic SB, in which
energetic electrons are accelerating in the shell. The age is much older than
that of SN 1006, and hence the particle acceleration time in this SB may be
longer than those in normal shell-like SNRs. We found point-like sources
associated with some of tight star clusters. The X-ray luminosity and spectrum
are consistent with those of young clusters of massive stars. Point-like
sources with non-thermal spectra are also found in the SB. These may be
background objects (AGNs) or stellar remnants (neutron stars or black holes).Comment: 11 pages, 6 figures, Accepted for publication in ApJ, the paper with
full resolution images in
http://www-cr.scphys.kyoto-u.ac.jp/member/bamba/Paper/30DorC.pd
Coherent radiation from neutral molecules moving above a grating
We predict and study the quantum-electrodynamical effect of parametric
self-induced excitation of a molecule moving above the dielectric or conducting
medium with periodic grating. In this case the radiation reaction force
modulates the molecular transition frequency which results in a parametric
instability of dipole oscillations even from the level of quantum or thermal
fluctuations. The present mechanism of instability of electrically neutral
molecules is different from that of the well-known Smith-Purcell and transition
radiation in which a moving charge and its oscillating image create an
oscillating dipole.
We show that parametrically excited molecular bunches can produce an easily
detectable coherent radiation flux of up to a microwatt.Comment: 4 page
ACTIVE DYNAMICS OF THE ENZYMES OF THE ANTIRADICAL PROTECTION AND THE GENERAL ANTIOXIDATIVE ACTIVITY BY THE DEVELOPMENT OF THE EXPERIMENTAL ISCHEMIC REPERFUSION OF LIVER
The purpose of the study: to research the active changes in several enzymes of the antioxidative protection within the dynamical development of the liver reperfusion in rats. Materials and methods: the study has been performed on 95 white non-lineal male rats with the mass of 240-280 g divided into groups, the biological material of which has been sampled within 5-20 minutes of the ischemic period and 5-20 minutes of the reperfusion period with the interval of 5 minutes. To evaluate the changes of the antioxidative system the activity of the superoxide dismutase, the erythrocyte catalase and the liver homogenate as well as the general antioxidative activity have been determined. Results: the performed study has demonstrated the imbalance development for the relation between the activity of catalase and superoxide dismutase by the development of the ischemic reperfusion syndrome with the change of this relation to the prevalence of the catalase activity on the systemic level and the superoxide dismutase activity on the organic level after the circulatory restoration. Besides the increase in activity of the studied enzymes from the erythrocyte, meal by 2 times in comparison with the control group has been determined especially at the ischemic period as well as the tendencies to the progressive activity decrease of the same enzymes in the liver tissue. The general antioxidative activity in the period of ischemic reperfusion has been decreasing to the fifth minute of ischemia by 2 times and has lasted on the same level (0.04-0.05 mg/l of vitamin C in terms of 1 gram of homogenate protein) during the entire experiment. Conclusion: the received results have demonstrated the possibility for the evaluation of the functional state for the system of oxidative restorative homeostasis in an animal by ischemic reperfusion of the liver against the background of the lowered general antioxidative activity. It was marked also the necessity of the metabolic support of this link within the system of non-specific resistance for the correction of the developing disorders
Spontaneous current generation in gated nanostructures
We have observed an unusual dc current spontaneously generated in the
conducting channel of a short-gated GaAs transistor. The magnitude and
direction of this current critically depend upon the voltage applied to the
gate. We propose that it is initiated by the injection of hot electrons from
the gate that relax via phonon emission. The phonons then excite secondary
electrons from asymmetrically distributed impurities in the channel, which
leads to the observed current
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