1,031 research outputs found
Uniaxial aerodynamic attitude control of artificial satellites
Within the context of a simple mechanical model the paper examines the movement of a satellite with respect to the center of masses under conditions of uniaxial aerodynamic attitude control. The equations of motion of the satellite take account of the gravitational and restorative aerodynamic moments. It is presumed that the aerodynamic moment is much larger than the gravitational, and the motion equations contain a large parameter. A two-parameter integrated surface of these equations is constructed in the form of formal series in terms of negative powers of the large parameter, describing the oscillations and rotations of the satellite about its lengthwise axis, approximately oriented along the orbital tangent. It is proposed to treat such movements as nominal undisturbed motions of the satellite under conditions of aerodynamic attitude control. A numerical investigation is made for the above integrated surface
Propagation Effects in Magnetized Transrelativistic Plasmas
The transfer of polarized radiation in magnetized and non-magnetized
relativistic plasmas is an area of research with numerous flaws and gaps. The
present paper is aimed at filling some gaps and eliminating the flaws. Starting
from a Trubnikov's linear response tensor for a vacuum wave with in thermal plasma, the analytic expression for the dielectric
tensor is found in the limit of high frequencies. The Faraday rotation and
Faraday conversion measures are computed in their first orders in the ratio of
the cyclotron frequency to the observed frequency . The
computed temperature dependencies of propagation effects bridge the known
non-relativistic and ultra-relativistic limiting formulas. The fitting
expressions are found for high temperatures, where the higher orders in
cannot be neglected. The plasma eigenmodes are found to
become linearly polarized at much larger temperatures than thought before. The
results are applied to the diagnostics of the hot ISM, hot accretion flows, and
jets.Comment: 7 pages, 7 figures, accepted by Ap
Optical transparency modes in anisotropic media
The modes of nonlinear propagation of the two-component electromagnetic
pulses through optically uniaxial media containing resonant particles are
studied. The features of their manifestation in the "dense" media and in the
media with expressed positive and negative birefringences are discussed. It is
shown that exponentially and rationally decreasing solutions of the system of
material and wave equations allow us also to describe the propagation of the
self-induced transparency pulses in isotropic media in the case, when the
direct electric dipole-dipole interaction between the resonant particles is
taken into account.Comment: LaTeX, 11 pages, 4 figures, International Conference on Coherent and
Nonlinear Optics (ICONO 2005
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
Circular Polarization from Gamma-ray Burst Afterglows
We investigate the circular polarization (CP) from Gamma-Ray Burst (GRB)
afterglows. We show that a tangled magnetic field cannot generate CP without an
ordered magnetic field because there is always an oppositely directed field, so
that no handedness exists. This implies the observation of CP could be a useful
probe of an ordered field, which carries valuable information on the GRB
central engine. By solving the transfer equation of polarized radiation, we
find that the CP reaches 1% at radio frequencies and 0.01% at optical for the
forward shock, and 10-1% at radio and 0.1-0.01% at optical for the reverse
shock.Comment: 12 pages, 3 figure
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
Probing the Magnetic Field Structure in Gamma-Ray Bursts through Dispersive Plasma Effects on the Afterglow Polarization
(Abr) The origin and structure of magnetic fields in Gamma-Ray Burst (GRB)
fireball plasmas are two of the most important open questions in all GRB
models. We show that the structure and strength of the magnetic field may be
constrained by radio and IR observations of the early afterglow, where plasma
effects on the polarization of propagating radiation are significant. We
calculate these propagation effects for cold and relativistic plasmas, and find
that in the presence of a uniform equipartition field the degree of linear
polarization is suppressed, and circular polarization prevails at low
frequencies, nu < 1-3 GHz, (2x10^11 Hz < nu < few x 10^14 Hz) in the forward
(reverse) shock. At higher frequencies linear polarization dominates. At the
frequency of the transition between circular and linear polarization, the net
level of polarization is minimal, ~10-20%. These features are nearly
independent of the circumburst density. The transition frequency is smaller by
a factor of ~10 when the uniform field is much weaker than equipartition. The
dependence of these results on viewing geometry, outflow collimation and
magnetic field orientation is discussed. When the configuration of the field is
entangled over length scales much smaller than the extent of the emitting
plasma, the aforementioned effects should not be observed and a linear
polarization at the few % level is expected. Polarimetric observations during
the early afterglow, and particularly of the reverse shock emission, may
therefore place strong constraints on the structure and strength of the
magnetic field within the fireball plasma.Comment: 12 pages, 6 figures. Accepted for publication in ApJ. Revised version
includes improved discussion of viewing and fireball geometry, with
implications to resulting polarizatio
Electron-ion coupling upstream of relativistic collisionless shocks
It is argued and demonstrated by particle-in-cell simulations that the
synchrotron maser instability could develop at the front of a relativistic,
magnetized shock. The instability generates strong low-frequency
electromagnetic waves propagating both upstream and downstream of the shock.
Upstream of the shock, these waves make electrons lag behind ions so that a
longitudinal electric field arises and the electrons are accelerated up to the
ion kinetic energy. Then thermalization at the shock front results in a plasma
with equal temperatures of electrons and ions. Downstream of the shock, the
amplitude of the maser-generated wave may exceed the strength of the
shock-compressed background magnetic field. In this case the shock-accelerated
particles radiate via nonlinear Compton scattering rather than via a
synchrotron mechanism. The spectrum of the radiation differs, in the
low-frequency band, from that of the synchrotron radiation, providing possible
observational tests of the model.Comment: 22 pages, 10 figures. To appear in ApJ vol. 65
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