847 research outputs found
Gamma-ray Flares and VLBI Outbursts of Blazars
A model is developed for the time dependent electromagnetic - radio to
gamma-ray - emission of active galactic nuclei, specifically, the blazars,
based on the acceleration and creation of leptons at a propagating
discontinuity or {\it front} of a Poynting flux jet. The front corresponds to a
discrete relativistic jet component as observed with
very-long-baseline-interferometry (VLBI). Equations are derived for the number,
momentum, and energy of particles in the front taking into account synchrotron,
synchrotron-self-Compton (SSC), and inverse-Compton processes as well as
photon-photon pair production. The apparent synchrotron, SSC, and
inverse-Compton luminosities as functions of time are determined. Predictions
of the model are compared with observations in the gamma, optical and radio
bands. The delay between the high-energy gamma-ray flare and the onset of the
radio is explained by self-absorption and/or free-free absorption by external
plasma. Two types of gamma-ray flares are predicted depending on pair creation
in the front.Comment: 11 pages, submitted to ApJ. 10 figures can be obtained from R.
Lovelace by sending postal address to [email protected]
Stability of the Magnetopause of Disk-Accreting Rotating Stars
We discuss three modes of oscillation of accretion disks around rotating
magnetized neutron stars which may explain the separations of the kilo-Hertz
quasi periodic oscillations (QPO) seen in low mass X-ray binaries. The
existence of these compressible, non-barotropic magnetohydrodynamic (MHD) modes
requires that there be a maximum in the angular velocity of
the accreting material larger than the angular velocity of the star ,
and that the fluid is in approximately circular motion near this maximum rather
than moving rapidly towards the star or out of the disk plane into funnel
flows. Our MHD simulations show this type of flow and profile.
The first mode is a Rossby wave instability (RWI) mode which is radially
trapped in the vicinity of the maximum of a key function at
. The real part of the angular frequency of the mode is
, where is the azimuthal mode number.
The second mode, is a mode driven by the rotating, non-axisymmetric component
of the star's magnetic field. It has an angular frequency equal to the star's
angular rotation rate . This mode is strongly excited near the radius
of the Lindblad resonance which is slightly outside of . The third mode
arises naturally from the interaction of flow perturbation with the rotating
non-axisymmetric component of the star's magnetic field. It has an angular
frequency . We suggest that the first mode with is associated
with the upper QPO frequency, ; that the nonlinear interaction of the
first and second modes gives the lower QPO frequency, ;
and that the nonlinear interaction of the first and third modes gives the lower
QPO frequency , where .Comment: 10 pages, 7 figure
PRS27 One-Year Cost-Effectiveness of Montelukast in 2-6-Year-Old Children With Mild-Moderate Persistent Asthma in Belarus
Conductivity, weak ferromagnetism and charge instability in single crystal
The temperature dependence of resistivity, magnetization and electron-spin
resonance of the single crystal were measured in temperature
range of . Magnetization hysteresis in applied magnetic field
up to 0.7 T at , irreversible temperature behavior of
magnetization and resistivity were found . The obtained data were explained in
terms of degenerate tight binding model using random phase approximation. The
contribution of holes in and bands of manganese ions to the
conductivity, optical absorbtion spectra and charge instability in were studied. Charge susceptibility maxima resulted from the competition of
the on-site Coulomb interaction between the holes in different orbitals and
small hybridization of sub-bands were calculated at .Comment: 6 pages, 12 figure
Coronal structure of the cTTS V2129 Oph
The nature of the magnetic coupling between T Tauri stars and their disks
determines not only the mass accretion process but possibly the spin evolution
of the central star. We have taken a recently-published surface magnetogram of
one moderately-accreting T Tauri star (V2129 Oph) and used it to extrapolate
the geometry of its large-scale field. We determine the structure of the open
(wind-bearing) field lines, the closed (X-ray bright) field lines and those
potentially accreting field lines that pass through the equatorial plane inside
the Keplerian co-rotation radius. We consider a series of models in which the
stellar magnetic field is opened up by the outward pressure of the hot coronal
gas at a range of radii. As this radius is increased, accretion takes place
along simpler field structures and impacts on fewer sites at the stellar
surface. This is consistent with the observed variation in the Ca II IRT and
HeI lines which suggests that accretion in the visible hemisphere is confined
to a single high-latitude spot. By determining the density and velocity of the
accretion flows, we find that in order to have most of the total mass accretion
rate impacting on a single high-latitude region we need disk material to
accrete from approximately 7R*, close to the Keplerian co-rotation radius at
6.8R*. We also calculate the coronal density and X-ray emission measure. We
find that both the magnitude and rotational modulation of the emission measure
increase as the source surface is increased. For the field structure of V2129
Oph which is dominantly octupolar, the emission forms a bright, high-latitude
ring that is always in view as the star rotates. Since the accretion funnels
are not dense enough to cause significant scattering of coronal X-ray photons,
they provide only a low rotational modulation of around 10% at most.Comment: 10 pages, 9 figure
Particle Acceleration and Magnetic Dissipation in Relativistic Current Sheet of Pair Plasmas
We study linear and nonlinear development of relativistic and
ultrarelativistic current sheets of pair plasmas with antiparallel magnetic
fields. Two types of two-dimensional problems are investigated by
particle-in-cell simulations. First, we present the development of relativistic
magnetic reconnection, whose outflow speed is an order of the light speed c. It
is demonstrated that particles are strongly accelerated in and around the
reconnection region, and that most of magnetic energy is converted into
"nonthermal" part of plasma kinetic energy. Second, we present another
two-dimensional problem of a current sheet in a cross-field plane. In this
case, the relativistic drift kink instability (RDKI) occurs. Particle
acceleration also takes place, but the RDKI fast dissipates the magnetic energy
into plasma heat. We discuss the mechanism of particle acceleration and the
theory of the RDKI in detail. It is important that properties of these two
processes are similar in the relativistic regime of T > mc^2, as long as we
consider the kinetics. Comparison of the two processes indicates that magnetic
dissipation by the RDKI is more favorable process in the relativistic current
sheet. Therefore the striped pulsar wind scenario should be reconsidered by the
RDKI.Comment: To appear in ApJ vol. 670; 60 pages, 27 figures; References and typos
are fixe
PCV105 Pharmacoeconomic Analysis Of Rosuvastatin Use In Patients With Hypercholesterolemia In The Health Care Of Belarus
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