651 research outputs found
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
The V-mode polarization of the Cosmic Microwave Background
The V-mode polarization of the Cosmic Microwave Background is discussed in a
weakly magnetized plasma. The VV and VT angular power spectra are computed for
adiabatic initial conditions of the Einstein-Boltzmann hierarchy. Depending
upon the frequency channel and upon the magnetic field intensity, the VT power
spectra of the circular polarization can even be seven orders of magnitude
larger than a putative B-mode polarization stemming from the lensing of the
primary anisotropies. Specific programs aimed at the direct detection of the
V-mode polarization of the Cosmic Microwave Background could provide a new
observational tool for the scrutiny of pre-decoupling physics.Comment: 9 pages, 4 included figures; minor corrections to match the published
versio
New Kinds of Acoustic Solitons
We find that the modified sine-Gordon equation belonging to the class of the
soliton equations describes the propagation of extremely short transverse
acoustic pulses through the low-temperature crystal containing paramagnetic
impurities with effective spin S=1/2 in the Voigt geometry case. The features
of nonlinear dynamics of strain field and effective spins, which correspond to
the different kinds of acoustic solitons, are studied.Comment: 9 pages, 1 figur
A hard X-ray survey of the Crux Galactic spiral arm tangent. A catalog of sources
This work is part of a large solid angle hard X-ray survey. We analized a
number of observations by the IBIS telescope aboard the INTEGRAL observatory
covering the Crux Galactic spiral arm tangent. We have detected 46 hard X-ray
sources, with 15 of them being new. Among the identified sources there are 12
AGNs, 11 HMXBs, 6 LMXBs and 2 active stars. 13 sources remain unidendified.Comment: Accepted for publication in Astronomy Letter
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
Low temperature magnetic structure of CeRhIn by neutron diffraction on absorption-optimized samples
Two aspects of the ambient pressure magnetic structure of heavy fermion
material CeRhIn have remained under some debate since its discovery:
whether the structure is indeed an incommensurate helix or a spin density wave,
and what is the precise magnitude of the ordered magnetic moment. By using a
single crystal sample optimized for hot neutrons to minimize neutron absorption
by Rh and In, here we report an ordered moment of . In
addition, by using spherical neutron polarimetry measurements on a similar
single crystal sample, we have confirmed the helical nature of the magnetic
structure, and identified a single chiral domain
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
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