1,608 research outputs found
PULSARS WITH STRONG MAGNETIC FIELDS: POLAR GAPS, BOUND PAIR CREATION AND NONTHERMAL LUMINOSITIES
Modifications to polar-gap models for pulsars are discussed for the case
where the surface magnetic field, , of the neutron star is strong. For
B\ga4\times10^8\rm\,T, the curvature -quanta emitted tangentially to
the curved force lines of the magnetic field are captured near the threshold of
bound pair creation and are channelled along the magnetic field as bound
electron-positron pairs (positronium). The stability of such bound pairs
against ionization by the parallel electric field, , in the polar
cap, and against photoionization is discussed. Unlike free pairs, bound pairs
do not screen near the neutron star. As a consequence, the energy
flux in highly relativistic particles and high-frequency (X-ray and/or
-ray) radiation from the polar gaps can be much greater than in the
absence of positronium formation. We discuss this enhancement for (a)
Arons-type models, in which particles flow freely from the surface, and find
any enhancement to be modest, and (b) Ruderman-Sutherland-type models, in which
particles are tightly bound to the surface, and find that the enhancement can
be substantial. In the latter case we argue for a self-consistent,
time-independent model in which partial screening of maintains it
close to the threshold value for field ionization of the bound pairs, and in
which a reverse flux of accelerated particles maintains the polar cap at a
temperature such that thermionic emission supplies the particles needed for
this screening. This model applies only in a restricted range of periods,
, and it implies an energy flux in high-energy particles that can
correspond to a substantial fraction of the spin-down power of the pulsar.
Nonthermal, high-frequency radiation has been observed from six radio pulsarsComment: TEX file, 47 pages. Accepted by Australian J. Phy
Transition radiation in the quantum regime as a diffractive phenomenon
We demonstrate that the transition photon radiation and pair creation can be
interpreted as a diffractive phenomenon in terms of the light-cone wave
functions in a way similar to the Good-Walker approach [6] to the diffraction
dissociation. Our formulas for spectra agree with those obtained by Baier and
Katkov [5] within the quasiclassical operator method. However, there is some
disagreement with earlier results by Garibyan [4].Comment: 7 pages. The journal version published in Phys. Lett.
Structure of pair winds from compact objects with application to emission from bare strange stars
We present the results of numerical simulations of stationary, spherically
outflowing, electron-positron pair winds, with total luminosities in the range
10^{34}- 10^{42} ergs/s. In the concrete example described here, the wind
injection source is a hot, bare, strange star, predicted to be a powerful
source of electron-positron pairs created by the Coulomb barrier at the quark
surface. We find that photons dominate in the emerging emission, and the
emerging photon spectrum is rather hard and differs substantially from the
thermal spectrum expected from a neutron star with the same luminosity. This
might help distinguish the putative bare strange stars from neutron stars.Comment: 4 pages, 6 figures, 1 table, added references, to appear in the
proceedings of the conference "Isolated Neutron Stars: from the Surface to
the Interior", London, UK, 24-28 April 200
Tunable pinning of a superconducting vortex a by a magnetic vortex
The interaction between a straight vortex line in a superconducting film and
a soft magnetic nanodisk in the magnetic vortex state in the presence of a
magnetic field applied parallel to the film surfaces is studied theoretically.
The superconductor is described by London theory and the nanodisk by the
Landau-Lifshitz continuum theory of magnetism, using the approximation known as
the rigid vortex model. Pinning of the vortex line by the nanodisk is found to
result, predominantly, from the interaction between the vortex line and the
changes in the nanodisk magnetization induced by the magnetic field of the
vortex line and applied field. In the context of the rigid vortex model, these
changes result from the displacement of the magnetic vortex. This displacement
is calculated analytically by minimizing the energy, and the pinning potential
is obtained. The applied field can tune the pinning potential by controlling
the displacement of the magnetic vortex. The nanodisk magnetization curve is
predicted to change in the presence of the vortex lineComment: 9 pages, 8 figures. Submitted to Phys. Rev.
Thermal Evolution and Light Curves of Young Bare Strange Stars
The cooling of a young bare strange star is studied numerically by solving
the equations of energy conservation and heat transport for both normal and
superconducting strange quark matter inside the star. We show that the thermal
luminosity from the strange star surface, due to both photon emission and e+e-
pair production, may be orders of magnitude higher than the Eddington limit,
for about one day for normal quark matter but possibly for up to a hundred
years for superconducting quark matter, while the maximum of the photon
spectrum is in hard X-rays with a mean energy of ~ 100 keV or even more. This
differs both qualitatively and quantitatively from the photon emission from
young neutron stars and provides a definite observational signature for bare
strange stars. It is shown that the energy gap of superconducting strange quark
matter may be estimated from the light curves if it is in the range from ~ 0.5
MeV to a few MeV.Comment: Ref [10] added and abstract shortened. 4 pages, 3 figures, revtex4.
To be published in Phys. Rev. Letter
Кримінально-правова характеристика суб’єкта розголошення державної таємниці
Усов, Д. С. Кримінально-правова характеристика суб’єкта розголошення державної таємниці / Д. С. Усов // Вісник Кримінологічної асоціації України. - 2013. - № 3. - С. 251-258.В даній статті здійснений аналіз суб’єкту злочину та його
обов’язкових ознак, а саме: фізична особа, осудна особа та вік кримінальної відповідальності; розглянуто приналежність суб’єкта розголошення державної таємниці до спеціальних суб’єктів; а також, на підставі загальнотеоретичних положень, обґрунтовано визначення
суб’єкту розголошення державної таємниці.In this paper carried out an analysis of the perpetrator and his essential
characteristics, such as: an individual, a person of sound mind and age of
criminal responsibility, a subject considered accessory disclosing state secrets
in specific subjects, and on the basis of the general theoretical positions,
accurate identification of the subject disclosure of state secrets.В данной статье осуществлен анализ субъекта преступления и его
обязательных признаков, а именно: физическое лицо, вменяемое лицо и
возраст уголовной ответственности; рассмотрены принадлежность
субъекта разглашение государственной тайны к специальным субъектам, а также, на основании общетеоретических положений, обосновано определение субъекта разглашения государственной тайны
Nanoscale Zeeman localization of charge carriers in diluted magnetic semiconductor-permalloy hybrids
We investigate the possibility of charge carrier localization in magnetic
semiconductors due to the presence of a highly inhomogeneous external magnetic
field. As an example, we study in detail the properties of a magnetic
semiconductor-permalloy disk hybrid system. We find that the giant Zeeman
respose of the magnetic semiconductor in conjuction with the highly non-uniform
magnetic field created by the vortex state of a permalloy disk can lead to
Zeeman localized states at the interface of the two materials. These trapped
state are chiral, with chirality controlled by the orientation of the core
magnetization of the permalloy disk. We calculate the energy spectrum and the
eigenstates of these Zeeman localized states, and discuss their experimental
signatures in spectroscopic probes.Comment: 4 pages, 1 figur
High-Energy Emission From Millisecond Pulsars
The X-ray and gamma-ray spectrum of rotation-powered millisecond pulsars is
investigated in a model for acceleration and pair cascades on open field lines
above the polar caps. Although these pulsars have low surface magnetic fields,
their short periods allow them to have large magnetospheric potential drops,
but the majority do not produce sufficient pairs to completely screen the
accelerating electric field. The accelerating particles maintain high Lorentz
factors and undergo cyclotron resonant absorption of radio emission, that
produces and maintains a large pitch angle, resulting in a strong synchrotron
component. The resulting spectra consist of several distinct components:
curvature radiation from primary electrons dominating from 1 - 100 GeV,
synchrotron radiation from primary and secondary electrons dominating up to
about 100 MeV, and much weaker inverse-Compton radiation from primary electrons
at 0.1 - 1 TeV. We find that the relative size of these components depends on
pulsar period, period derivative, and neutron star mass and radius with the
level of the synchrotron component also depending sensitively on the radio
emission properties. This model is successful in describing the observed X-ray
and gamma-ray spectrum of PSR J0218+4232 as synchrotron radiation, peaking
around 100 MeV and extending up to a turnover around several GeV. The predicted
curvature radiation components from a number of millisecond pulsars, as well as
the collective emission from the millisecond pulsars in globular clusters,
should be detectable with AGILE and GLAST. We also discuss a hidden population
of X-ray-quiet and radio-quiet millisecond pulsars which have evolved below the
pair death line, some of which may be detectable by telescopes sensitive above
1 GeV.Comment: 34 pages, 6 figures, accepted for publication in Astrophysical
Journa
Coulomb crystals in the magnetic field
The body-centered cubic Coulomb crystal of ions in the presence of a uniform
magnetic field is studied using the rigid electron background approximation.
The phonon mode spectra are calculated for a wide range of magnetic field
strengths and for several orientations of the field in the crystal. The phonon
spectra are used to calculate the phonon contribution to the crystal energy,
entropy, specific heat, Debye-Waller factor of ions, and the rms ion
displacements from the lattice nodes for a broad range of densities,
temperatures, chemical compositions, and magnetic fields. Strong magnetic field
dramatically alters the properties of quantum crystals. The phonon specific
heat increases by many orders of magnitude. The ion displacements from their
equilibrium positions become strongly anisotropic. The results can be relevant
for dusty plasmas, ion plasmas in Penning traps, and especially for the crust
of magnetars (neutron stars with superstrong magnetic fields G). The effect of the magnetic field on ion displacements in a
strongly magnetized neutron star crust can suppress the nuclear reaction rates
and make them extremely sensitive to the magnetic field direction.Comment: 25 pages, 8 figures; accepted to Phys. Rev.
Induced scattering of short radio pulses
Effect of the induced Compton and Raman scattering on short, bright radio
pulses is investigated. It is shown that when a single pulse propagates through
the scattering medium, the effective optical depth is determined by the
duration of the pulse but not by the scale of the medium. The induced
scattering could hinder propagation of the radio pulse only if close enough to
the source a dense enough plasma is presented. The induced scattering within
the relativistically moving source places lower limits on the Lorentz factor of
the source. The results are applied to the recently discovered short
extragalactic radio pulse.Comment: submitted to Ap
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