59 research outputs found
Physics of Interpulse Emission in Radio Pulsars
The magnetized induced Compton scattering off the particles of the
ultrarelativistic electron-positron plasma of pulsar is considered. The main
attention is paid to the transverse regime of the scattering, which holds in a
moderately strong magnetic field. We specifically examine the problem on
induced transverse scattering of the radio beam into the background, which
takes place in the open field line tube of a pulsar. In this case, the
radiation is predominantly scattered backwards and the scattered component may
grow considerably. Based on this effect, we for the first time suggest a
physical explanation of the interpulse emission observed in the profiles of
some pulsars. Our model can naturally account for the peculiar spectral and
polarization properties of the interpulses. Furthermore, it implies a specific
connection of the interpulse to the main pulse, which may reveal itself in the
consistent intensity fluctuations of the components at different timescales.
Diverse observational manifestations of this connection, including the moding
behavior of PSR B1822-09, the peculiar temporal and frequency structure of the
giant interpulses in the Crab pulsar, and the intrinsic phase correspondence of
the subpulse patterns in the main pulse and the interpulse of PSR B1702-19, are
discussed in detail. It is also argued that the pulse-to-pulse fluctuations of
the scattering efficiency may lead to strong variability of the interpulse,
which is yet to be studied observationally. In particular, some pulsars may
exhibit transient interpulses, i.e. the scattered component may be detectable
only occasionally.Comment: 28 pages, 2 figures. Accepted for publication in Ap
Radial growth of functions from the Korenblum space
We study radial behavior of analytic and harmonic functions, which admit a
certain majorant in the unit disk. We prove that extremal growth or decay may
occur only along small sets of radii and give precise estimates of these
exceptional sets.Comment: 18 page
On the Axisymmetric Force-Free Pulsar Magnetosphere
We investigate the axisymmetric magnetosphere of an aligned rotating magnetic
dipole surrounded by an ideal force-free plasma. We concentrate on the magnetic
field structure around the point of intersection of the separatrix between the
open and closed field-line regions and the equatorial plane. We first study the
case where this intersection point is located at the Light Cylinder. We find
that in this case the separatrix equilibrium condition implies that all the
poloidal current must return to the pulsar in the open-field region, i.e., that
there should be no finite current carried by the separatrix/equator current
sheet. We then perform an asymptotic analysis of the pulsar equation near the
intersection point and find a unique self-similar solution; however, a Light
Surface inevitably emerges right outside the Light Cylinder. We then perform a
similar analysis for the situation where the intersection point lies somewhere
inside the Light Cylinder, in which case a finite current flowing along the
separatrix and the equator is allowed. We find a very simple behavior in this
case, characterized by a 90-degree angle between the separatrix and the equator
and by finite vertical field in the closed-field region. Finally, we discuss
the implications of our results for global numerical studies of pulsar
magnetospheres.Comment: 31 pages, including 5 figure
Disk Diffusion Propagation Model for the Outburst of XTE J1118+480
We present a linear diffusion model for the evolution of the double-peaked
outburst in the transient source XTEJ1118+480. The model treats the two
outbursts as episodic mass deposition at the outer radius of the disk followed
by evolution of disk structure according to a diffusion process. We demonstrate
that light curves with fast-rise, exponential decay profile are a general
consequence of the diffusion process. Deconvolution of the light curve proves
to be feasible and gives an input function specifying mass deposition at the
outer disk edge as well as the total mass of the disk, both as functions of
time. The derived evolution of total disk mass can be correlated with the
observed evolution of the ~0.1 Hz QPO in the source reported in Wood et al.
(2000).Comment: 26 pages, 6 figures, accepted for publication in Ap
Interpretation of the Low-Frequency Peculiarities in the Radio Profile Structure of the Crab Pulsar
The theory of magnetized induced scattering off relativistic gyrating
particles is developed. It is directly applicable to the magnetosphere of a
pulsar, in which case the particles acquire gyration energies as a result of
resonant absorption of radio emission. In the course of the radio beam
scattering into background the scattered radiation concentrates along the
ambient magnetic field. The scattering from different harmonics of the particle
gyrofrequency takes place at different characteristic altitudes in the
magnetosphere and, because of the rotational effect, gives rise to different
components in the pulse profile. It is demonstrated that the induced scattering
from the first harmonic into the state under the resonance can account for the
so-called low-frequency component in the radio profile of the Crab pulsar. The
precursor component is believed to result from the induced scattering between
the two states well below the resonance. It is shown that these ideas are
strongly supported by the polarization data observed. Based on an analysis of
the fluctuation behaviour of the scattering efficiencies, the transient
components of a similar nature are predicted for other pulsars.Comment: 9 pages, no figures. Accepted for publication in MNRA
On the Nature of Precursors in the Radio Pulsar Profiles
In the average profiles of several radio pulsars, the main pulse is
accompanied by the preceding component. This so called precursor is known for
its distinctive polarization, spectral, and fluctuation properties. Recent
single-pulse observations hint that the sporadic activity at the extreme
leading edge of the pulse may be prevalent in pulsars. We for the first time
propose a physical mechanism of this phenomenon. It is based on the induced
scattering of the main pulse radiation into the background. We show that the
scattered component is directed approximately along the ambient magnetic field
and, because of rotational aberration in the scattering region, appears in the
pulse profile as a precursor to the main pulse. Our model naturally explains
high linear polarization of the precursor emission, its spectral and
fluctuation peculiarities as well as suggests a specific connection between the
precursor and the main pulse at widely spaced frequencies. This is believed to
stimulate multifrequency single-pulse studies of intensity modulation in
different pulsars.Comment: 5 pages, no figures. Accepted for publication in MNRAS Letter
On the nature of the variability power decay towards soft spectral states in X-ray binaries. Case study in Cyg X-1
A characteristic feature of the Fourier Power Density Spectrum (PDS) observed
from black hole X-ray binaries in low/hard and intermediate spectral states is
a broad band-limited noise, characterized by a constant below some frequency (a
``break'' frequency) and a power law above this frequency. It has been shown
that the variability of this type can be produced by the inward diffusion of
the local driving perturbations in a bounded configuration (accretion disk or
corona). In the framework of this model, the perturbation diffusion time t_0 is
related to the phenomenological break frequency, while the PDS power-law slope
above the ``break'' is determined by the viscosity distribution over the
configuration. he perturbation diffusion scenario explains the decay of the
power of X-ray variability observed in a number of compact sources (containing
black hole and neutron star) during an evolution of theses sources from
low/hard to high/soft states. We compare the model predictions with the subset
of data from Cyg X-1 collected by the Rossi X-ray Time Explorer (RXTE). Our
extensive analysis of the Cyg X-1 PDSs demonstrates that the observed
integrated power P_x decreases approximately as a square root of the
characteristic frequency of the driving oscillations \nu_{dr}. The RXTE
observations of Cyg X-1 allow us to infer P_{dr} and t_0 as a function of
\nu_{dr}. Using the inferred dependences of the integrated power of the driving
oscillations P_{dr} and t_0 on \nu_{dr} we demonstrate that the power predicted
by the model also decays as P_{x,diff} proportional to \nu_{dr}^{-0.5} that is
similar to the observed P_{x} behavior.Comment: 15 page, 5 figures, accepted for publication in the Astrophysical
Journa
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
Transformation of the Poynting flux into the kinetic energy in relativistic jets
The acceleration of relativistic jets from the Poynting to the matter
dominated stage is considered. The are generally two collimation regimes, which
we call equilibrium and non-equilibrium, correspondingly. In the first regime,
the jet is efficiently accelerated till the equipartition between the kinetic
and electro-magnetic energy. We show that after the equilibrium jet ceases to
be Poynting dominated, the ratio of the electro-magnetic to the kinetic energy
decreases only logarithmically so that such jets become truly matter dominated
only at extremely large distances. Non-equilibrium jets remain generally
Poynting dominated till the logarithmically large distances. In the only case
when a non-equilibrium jet is accelerated till the equipartition level, we
found that the flow is not continued to the infinity but is focused towards the
axis at a finite distance from the origin.Comment: Submitted to MNRAS Minor changes in the Conclusion
Very-high-energy gamma radiation associated with the unshocked wind of the Crab pulsar
We show that the relativistic wind in the Crab pulsar, which is commonly
thought to be invisible in the region upstream of the termination shock at R <
0.1 pc, in fact could be directly observed through its inverse Compton gamm-ray
emission. The search for such specific component of radiation in the gamma-ray
spectrum of the Crab can provide unique information about the unshocked pulsar
wind that is not accessible at other wavelengths.Comment: 11 pages, 11 figures, to appear in one of the April issues of MNRA
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