280 research outputs found
On the self-consistent model of the axisymmetric radio pulsar magnetosphere
We consider a model of axisymmetric neutron star magnetosphere. In our
approach, the current density in the region of open field lines is constant and
the returning current flows in a narrow layer along the separatrix. In this
case, the stream equation describing the magnetic field structure is linear
both in the open and closed regions, the main problem lying in matching the
solutions along the separatrix (Okamoto 1974; Lyubarskii 1990). We demonstrate
that it is the stability condition on the separatrix that allows us to obtain a
unique solution of the problem. In particular, the zero point of magnetic field
is shown to locate near the light cylinder. Moreover, the hypothesis of the
existence of the nonlinear Ohm's Law (Beskin, Gurevich & Istomin 1983)
connecting the potential drop in the pair creation region and the longitudinal
electric current flowing in the magnetosphere is confirmed.Comment: 7 pages, 5 figures, twocolumn MNRAS styl
On the role of the current loss in radio pulsar evolution
The aim of this article is to draw attention to the importance of the
electric current loss in the energy output of radio pulsars. We remind that
even the losses attributed to the magneto-dipole radiation of a pulsar in
vacuum can be written as a result of an Ampere force action of the electric
currens flowing over the neutron star surface (Michel, 1991, Beskin et al.,
1993). It is this force that is responsible for the transfer of angular
momentum of a neutron star to an outgoing magneto-dipole wave. If a pulsar is
surrounded by plasma, and there is no longitudinal current in its
magnetosphere, there is no energy loss (Beskin et al., 1993, Mestel et al.,
1999). It is the longitudinal current closing within the pulsar polar cap that
exerts the retardation torque acting on the neutron star. This torque can be
determined if the structure of longitudinal current is known. Here we remind of
the solution by Beskin, Gurevitch & Istomin (1993) and discuss the validity of
such an assumption. The behavior of the recently observed "part-time job"
pulsar B1931+24 can be naturally explained within the model of current loss
while the magneto-dipole model faces difficulties.Comment: 4 pages, to appear in Astrophysics and Space Science, Special Issue:
Isolated Neutron Stars. In the replaced paper we amended several misprints
(coefficients in equations 12,14,15) and removed the excessive explanation
for the boundary condition (4
On the Possibility of the Detection of Extinct Radio Pulsars
We explore the possibilities for detecting pulsars that have ceased to
radiate in the radio band. We consider two models: the model with hindered
particle escape from the pulsar surface (first suggested by Ruderman and
Sutherland 1975) and the model with free particle escape (Arons 1981; Mestel
1999). In the model with hindered particle escape, the number of particles that
leave the pulsar magnetosphere is small and their radiation cannot be detected
with currently available instruments. At the same time, for the free particle
escape model, both the number of particles and the radiation intensity are high
enough for such pulsars to be detectable with the presently available receivers
such as GLAST and AGILE spacecrafts. It is also possible that extinct radio
pulsars can be among the unidentified EGRET sources.Comment: 5 pages, 1 figure corrected version of the paper that was published
in Astronomy Letter
Peculiar objects in the birthplaces of radio pulsars -- stellar-mass black hole candidates
We perform a search for stellar-mass black hole candidates in the spatial
regions with increased probability of their occurrence, isolated based on the
evolutionary scenarios for compact objects originating in disrupted binaries.
We analyze the sources located in these regions with available spectral or
photometric data, as well as measured proper motions and distances. Nine
objects that exhibit characteristics corresponding to theoretical predictions
for isolated black holes are marked for further study as black hole candidates
Kinetic theory of electromagnetic ion waves in relativistic plasmas
A kinetic theory for electromagnetic ion waves in a cold relativistic plasma
is derived. The kinetic equation for the broadband electromagnetic ion waves is
coupled to the slow density response via an acoustic equation driven by
ponderomotive force like term linear in the electromagnetic field amplitude.
The modulational instability growth rate is derived for an arbitrary spectrum
of waves. The monochromatic and random phase cases are studied.Comment: 7 pages, 4 figures, to appear in Physics of Plasma
Statistics of Neutron Stars at the Stage of Supersonic Propeller
We analyze the statistical distribution of neutron stars at the stage of a
supersonic propeller. An important point of our analysis is allowance for the
evolution of the angle of inclination of the magnetic axis to the spin axis of
the neutron star for the boundary of the transition to the supersonic propeller
stage for two models: the model with hindered particle escape from the stellar
surface and the model with free particle escape. As a result, we have shown
that a consistent allowance for the evolution of the inclination angle in the
region of extinct radio pulsars for the two models leads to an increase in the
total number of neutron stars at the supersonic propeller stage. This increase
stems from he fact that when allowing for the evolution of the inclination
angle for neutron stars in the region of extinct radio pulsars and,
hence, for the boundary of the transition to the propeller stage, this
transition is possible at shorter spin periods (P~5-10 s) than assumed in the
standard model.Comment: 15 pages, 6 figures; scale corrected for figures 3-
M87 black hole mass and spin estimate through the position of the jet boundary shape break
We propose a new method of estimating a mass of a super massive black hole
residing in the center of an active galaxy. The active galaxy M87 offers a
convenient test case for the method due to the existence of a large amount of
observational data on the jet and ambient environment properties in the central
area of the object. We suggest that the observed transition of a jet boundary
shape from a parabolic to a conical form is associated with the flow transiting
from the magnetically dominated regime to the energy equipartition between
plasma bulk motion and magnetic field. By coupling the unique set of
observations available for the jet kinematics, environment and boundary profile
with our MHD modelling under assumption on the presence of a dynamically
important magnetic field in the M87 jet, we estimate the central black hole
mass and spin. The method leads us to believe that the M87 super massive black
hole has a mass somewhat larger than typically accepted so far.Comment: 10 pages, 1 figure, 3 tables, accepted for publication by MNRA
Region of the anomalous compression under Bondi-Hoyle accretion
We investigate the properties of an axisymmetric non-magnetized gas flow
without angular momentum on a small compact object, in particular, on a
Schwarzschild black hole in the supersonic region near the object; the velocity
of the object itself is assumed to be low compared to the speed of sound at
infinity. First of all, we see that the streamlines intersect (i.e., a caustic
forms) on the symmetry axis at a certain distance from the center on the
front side if the pressure gradient is neglected. The characteristic radial
size of the region, in which the streamlines emerging from the sonic surface at
an angle no larger than to the axis intersect, is To refine the flow structure in this region, we numerically
compute the system in the adiabatic approximation without ignoring the
pressure. We estimate the parameters of the inferred region with anomalously
high matter temperature and density accompanied by anomalously high energy
release.Comment: 10 pages, 2 figure
- …