448 research outputs found
Collective processes in relativistic plasma and their implications for gamma-ray burst afterglows
We consider the effects of collective plasma processes on synchrotron
emission from highly relativistic electrons. We find, in agreement with Sazonov
(1970), that strong effects are possible also in the absence of a
non-relativistic plasma component, due to the relativistic electrons (and
protons) themselves. In contrast with Sazonov, who infers strong effects only
in cases where the ratio of plasma frequency to cyclotron frequency is much
larger than the square of the characteristic electron Lorentz factor, nu_p/nu_B
>> gamma^2, we find strong effects also for 1 << nu_p/nu_B << gamma^2. The
modification of the spectrum is prominent at frequencies nu < nu_{R*} = nu_p
min[gamma, (nu_p/nu_B)^(1/2)], where nu_{R*} generalizes the Razin-Tsytovich
frequency, nu_R = gamma nu_p, to the regime nu_p/nu_B << gamma^2. Applying our
results to gamma-ray burst (GRB) plasmas, we predict a strong modification of
the radio spectrum on minute time scale following the GRB, at the onset of
fireball interaction with its surrounding medium, in cases where the ratio of
the energy carried by the relativistic electrons to the energy carried by the
magnetic field exceeds ~ 10^5. Plausible electron distribution functions may
lead to negative synchrotron reabsorption, i.e to coherent radio emission,
which is characterized by a low degree of circular polarization. Detection of
these effects would constrain the fraction of energy in the magnetic field,
which is currently poorly determined by observations, and, moreover, would
provide a novel handle on the properties of the environment into which the
fireball expands.Comment: 28 pages, 1 figure, submitted to Ap
Gravitational orientation of the orbital complex, Salyut-6--Soyuz
A simple mathematical model is proposed for the Salyut-6-Soyuz orbital complex motion with respect to the center of mass under the one-axis gravity-gradient orientation regime. This model was used for processing the measurements of the orbital complex motion parameters when the above orientation region was implemented. Some actual satellite motions are simulated and the satellite's aerodynamic parameters are determined. Estimates are obtained for the accuracy of measurements as well as that of the mathematical model
Quantum interference in the classically forbidden region: a parametric oscillator
We study tunneling between period two states of a parametrically modulated
oscillator. The tunneling matrix element is shown to oscillate with the varying
frequency of the modulating field. The effect is due to spatial oscillations of
the wave function and the related interference in the classically forbidden
region. The oscillations emerge already in the ground state of the oscillator
Hamiltonian in the rotating frame, which is quartic in the momentum.Comment: Submitted to PR
Multiphoton antiresonance in large-spin systems
We study nonlinear response of a spin with easy-axis anisotropy. The
response displays sharp dips or peaks when the modulation frequency is
adiabatically swept through multiphoton resonance. The effect is a consequence
of a special symmetry of the spin dynamics in a magnetic field for the
anisotropy energy . The occurrence of the dips or peaks is
determined by the spin state. Their shape strongly depends on the modulation
amplitude. Higher-order anisotropy breaks the symmetry, leading to sharp steps
in the response as function of frequency. The results bear on the dynamics of
molecular magnets in a static magnetic field.Comment: Submitted to PR
Luminosity Function of High-Mass X-ray Binaries and Anisotropy in the Distribution of Active Galactic Nuclei toward the Large Magellanic Cloud
In 2003-2012, the INTEGRAL observatory has performed long-term observations
of the Large Magellanic Cloud (LMC). At present, this is one of the deepest
hard X-ray (20-60 keV) surveys of extragalactic fields in which more than 20
sources of different natures have been detected. We present the results of a
statistical analysis of the population of high-mass X-ray binaries in the LMC
and active galactic nuclei (AGNs) observed in its direction. The hard X-ray
luminosity function of high-mass X-ray binaries is shown to be described by a
power law with a slope alpha~1.8, that in agreement with the luminosity
function measurements both in the LMC itself, but made in the soft X-ray energy
band, and in other galaxies. At the same time, the number of detected AGNs
toward the LMC turns out to be considerably smaller than the number of AGNs
registered in other directions, in particular, toward the source 3C 273. The
latter confirms the previously made assumption that the distribution of matter
in the local Universe is nonuniform.Comment: 5 pages, 5 figures, will be published in Astronomy Letters, 2012,
Vol. 38, No. 8, p. 492--49
Several New Active Galactic Nuclei Among X-ray Sources Detected by INTEGRAL and SWIFT Observatories
We present the results of the optical identifications of a set of X-ray
sources from the all-sky surveys of INTEGRAL and SWIFT observatories. Optical
data were obtained with Russian-Turkish 1.5-m Telescope (RTT150). Nine X-ray
sources were identified as active galactic nuclei (AGNs). Two of them are
hosted by nearby, nearly exactly edge-on, spiral galaxies MCG -01-05-047 and
NGC 973. One source, IGR J16562-3301, is most probably BL Lac object (blazar).
Other AGNs are observed as stellar-like nuclei of spiral galaxies, with broad
emission lines in their spectra.
For the majority of our hard X-ray selected AGNs, their hard X-ray
luminosities are well-correlated with the luminosities in [OIII],5007 optical
emission line. However, the luminosities of some AGNs deviate from this
correlation. The fraction of these objects can be as high as 20%. In
particular, the flux in [OIII] line turns to be lower in two nearby edge-on
spiral galaxies, which can be explained by the extinction in their galactic
disks.Comment: 9 pages, 3 figures, accepted for publication in Astronomy Letters,
the original text in Russian can be found at
http://hea.iki.rssi.ru/~rodion/poptid.pd
Optical Identification of Four Hard X-ray Sources from the Swift All-Sky Survey
We present the results of our optical identifications of four hard X-ray
sources from the Swift all-sky survey. We obtained optical spectra for each of
the program objects with the 6-m BTA telescope (Special Astrophysical
Observatory, Russian Academy of Sciences, Nizhnii Arkhyz), which allowed their
nature to be established. Two sources (SWIFT J2237.2+6324} and SWIFT
J2341.0+7645) are shown to belong to the class of cataclysmic variables
(suspected polars or intermediate polars). The measured emission line width
turns out to be fairly large (FWHM ~ 15-25 A), suggesting the presence of
extended, rapidly rotating (v~400-600 km/s) accretion disks in the systems.
Apart from line broadening, we have detected a change in the positions of the
line centroids for SWIFT J2341.0+7645, which is most likely attributable to the
orbital motion of the white dwarf in the binary system. The other two program
objects (SWIFT J0003.3+2737 and SWIFT J0113.8+2515) are extragalactic in
origin: the first is a Seyfert 2 galaxy and the second is a blazar at redshift
z=1.594. Apart from the optical spectra, we provide the X-ray spectra for all
sources in the 0.6-10 keV energy band obtained from XRT/Swift data.Comment: 9 pages, 6 figures, will be published in Astronomy Letters, 38, No.5,
pp.281-289 (2012
Optical Multicolor WBVR-Observations of the X-Ray Star V1341 Cyg = Cyg X-2 in 1986-1992
We present the results of observations of the low-mass X-ray binary
V1341 X--2. Our observations include a total of
2375 individual measurements in four bands on 478 nights in 1986-1992. We tied
the comparison and check stars used for the binary to the catalog using
their magnitudes. The uncertainty of this procedure was 3 in the
and bands and 8%-10% for the and bands. In quiescence, the
amplitude of the periodic component in the binary's brightness variations
is within ( in ); this is due
to the ellipsoidal shape of the optical component, which is distorted with
gravitational forces from the X-ray component. Some of the system's active
states (long flares) may be due to instabilities in the accretion disk, and
possibly to instabilities of gas flows and other accretion structures. The
binary possesses a low-luminosity accretion disk. The light curves reveal no
indications of an eclipse near the phases of the upper and lower conjunctions
in quiescence or in active states during the observed intervals. We conclude
that the optical star in the close binary V1341
X-2 is a red giant rather than a blue straggler. We studied the long-term
variability of the binary during the seven years covered by our observations.
The optical observations presented in this study are compared to X-ray data
from the Ginga observatory for the same time intervals.Comment: 35 pages, 8 figure
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