441 research outputs found
General Relativistic Effect of Gravitomagnetic Charge on Pulsar Magnetosphere and Particle Acceleration in a Polar Cap
We study magnetospheric structure surrounding rotating magnetized neutron
star with nonvanishing NUT (Newman-Tamburino-Unti) parameter. For the
simplicity of calculations Goldreich-Julian charge density is analyzed for the
aligned neutron star with zero inclination between magnetic field,
gravitomagnetic field and rotation axis. From the system of Maxwell equations
in spacetime of slowly rotating NUT star, second-order differential equation
for electrostatic potential is derived. Analytical solution of this equation
indicates the general relativistic modification of an accelerating electric
field and charge density along the open field lines by the gravitomagnetic
charge. The implication of this effect to the magnetospheric energy loss
problem is underlined. In the second part of the paper we derive the equations
of motion of test particles in magnetosphere of slowly rotating NUT star. Then
we analyze particle motion in the polar cap and show that NUT parameter can
significantly change conditions for particle acceleration.Comment: 21 pages, 6 figures, accepted for publication in Ap
Pulsar Polar Cap Heating and Surface Thermal X-Ray Emission I. Curvature Radiation Pair Fronts
We investigate the effect of pulsar polar cap (PC) heating produced by
positrons returning from the upper pair formation front. Our calculations are
based on a self-consistent treatment of the pair dynamics and the effect of
electric field screening by the returning positrons. We calculate the resultant
X-ray luminosities, and discuss the dependence of the PC heating efficiencies
on pulsar parameters, such as characteristic spin-down age, spin period, and
surface magnetic field strength. In this study we concentrate on the regime
where the pairs are produced in a magnetic field by curvature photons emitted
by accelerating electrons. Our theoretical results are not in conflict with the
available observational X-ray data and suggest that the effect of PC heating
should significantly contribute to the thermal X-ray fluxes from middle-aged
and old pulsars. The implications for current and future X-ray observations of
pulsars are briefly outlined.Comment: 28 pages, 7 figures, accepted for publication in Ap
Pair Multiplicities and Pulsar Death
Through a simple model of particle acceleration and pair creation above the
polar caps of rotation-powered pulsars, we calculate the height of the
pair-formation front (PFF) and the dominant photon emission mechanism for the
pulsars in the Princeton catalog. We find that for most low- and moderate-field
pulsars, the height of the pair formation front and the final Lorentz factor of
the primary beam is set by nonresonant inverse Compton scattering (NRICS), in
the Klein-Nishina limit. NRICS is capable of creating pairs over a wide range
of pulsar parameters without invoking a magnetic field more complicated than a
centered dipole, although we still require a reduced radius of curvature for
most millisecond pulsars. For short-period pulsars, the dominant process is
curvature radiation, while for extremely high-field pulsars, it is resonant
inverse Compton scattering (RICS). The dividing point between NRICS dominance
and curvature dominance is very temperature-dependent; large numbers of pulsars
dominated by NRICS at a stellar temperature of K are dominated by
curvature at K. We apply these results to pulsar death-line calculations
and to the issue of particle injection into the Crab Nebula.Comment: 14 pages, 7 figures, to appear in Ap
Effects of Rotation and Relativistic Charge Flow on Pulsar Magnetospheric Structure
We propose an analytical 3-D model of the open field-line region of a neutron
star (NS) magnetosphere. We construct an explicit analytic solution for
arbitrary obliquity (angle between the rotation and magnetic axes)
incorporating the effects of magnetospheric rotation, relativistic flow of
charges (e.g. primary electron beam) along the open field lines, and E X B
drift of these charges. Our solution employs the space-charge-limited
longitudinal current calculated in the electrodynamic model of Muslimov &
Tsygan (1992) and is valid up to very high altitudes nearly approaching the
light cylinder. We assume that in the innermost magnetosphere, the NS magnetic
field can be well represented by a static magnetic dipole configuration. At
high altitudes the open magnetic field lines significantly deviate from those
of a static dipole and tend to focus into a cylindrical bundle, swept back in
the direction opposite to the rotation, and also bent towards the rotational
equator. We briefly discuss some implications of our study to spin-powered
pulsars.Comment: 24 pages, 3 figures, accepted for publication in Ap
The Role of Media Resources in the Process of Self-Education
This article discusses media resources influence in self-education. Methods of formation of students' media-information competencies in the organization of self -education of students through media resources, ensuring their activity and independence in cognitive activity, the formation of professional skills, and the development of creative and critical thinking skills are covered. The technique proposed in media instruction models is more often than not based on cycles (pieces, modules) of imaginative and play errands that are effectively utilized by instructors in the course and out of course exercises
Particle Acceleration in Pair-Starved Pulsars
We investigate the physical situation above the pulsar polar cap (PC) where
the accelerating primaries (electrons) are not capable of producing sufficient
numbers of electron-positron pairs at low altitudes (within 1-2 stellar radii
above the PC surface) to screen the accelerating electric field, and continue
accelerating up to, at least, very high altitudes nearly approaching the light
cylinder. We derive an analytic solution for the parallel electric field valid
at high altitudes. The solution is based on the physical condition of
asymptotic vanishing of the rotationally induced transverse electric field
within the magnetic flux tube. This condition constrains the asymptotic value
of the effective space charge that determines the distribution of the parallel
electric field within the magnetic tube. Our estimates of low- to high-altitude
values of the parallel electric field imply the occurrence of a regime of
primary acceleration (with the characteristic Lorentz factor up to 1-2 X 10^7)
all the way from the PC to the light cylinder limited by curvature-radiation
reaction. In this model the primary outflow becomes asymptotically force-free,
and may turn into a relativistic wind beyond the light cylinder. Such a
solution will apply to both older pulsars producing only inverse Compton
scattering pairs and younger very high B pulsars (magnetars). We suggest that
pulsars, which are lying below the pair death line, may be radio-quiet
gamma-ray sources.Comment: 20 pages, accepted for publication in Ap
Gamma-ray emission from rotation-powered pulsars
Using a simplified model of cascade pair creation over pulsar polar caps
presented in two previous papers, we investigate the expected gamma-ray output
from pulsars' low altitude particle acceleration and pair creation regions. We
divide pulsars into several categories, based on which mechanism truncates the
particle acceleration off the polar cap, and give estimates for the expected
luminosity of each category.
We find that inverse Compton scattering above the pulsar polar cap provides
the primary gamma rays which initiate the pair cascades in most pulsars. This
reduces the expected -ray luminosity below previous estimates which
assumed curvature gamma ray emission was the dominant initiator of pair
creation in all pulsars.Comment: 10 pages, 5 figures, to be published in Ap
Pulsar Polar Cap Heating and Surface Thermal X-Ray Emission II. Inverse Compton Radiation Pair Fronts
We investigate the production of electron-positron pairs by inverse Compton
scattered (ICS) photons above a pulsar polar cap (PC) and surface heating by
returning positrons. This paper is a continuation of our self-consistent
treatment of acceleration, pair dynamics and electric field screening above
pulsar PCs. We calculate the altitude of the inverse Compton pair formation
fronts, the flux of returning positrons and present the heating efficiencies
and X-ray luminosities. We revise pulsar death lines implying cessation of pair
formation, and present them in surface magnetic field-period space. We find
that virtually all known radio pulsars are capable of producing pairs by
resonant and non-resonant ICS photons radiated by particles accelerated above
the PC in a pure star-centered dipole field, so that our ICS pair death line
coincides with empirical radio pulsar death. Our calculations show that ICS
pairs are able to screen the accelerating electric field only for high neutron
star surface temperatures and magnetic fields. We argue that such screening at
ICS pair fronts occurs locally, slowing but not turning off acceleration of
particles until screening can occur at a curvature radiation (CR) pair front at
higher altitude. In the case where no screening occurs above the PC surface, we
anticipate that the pulsar gamma-ray luminosity will be a substantial fraction
of its spin-down luminosity. The X-ray luminosity resulting from PC heating by
ICS pair fronts is significantly lower than the PC heating luminosity from CR
pair fronts, which dominates for most pulsars. PC heating from ICS pair fronts
is highest in millisecond pulsars, which cannot produce CR pairs, and may
account for observed thermal X-ray components in the spectra of these old
pulsars.Comment: 29 pages, 10 figures, accepted for publication in Ap
Pulsar X-Ray and Gamma-Ray Pulse Profiles: Constraint on Obliquity and Observer Angles
We model the thermal X-ray profiles of Geminga, Vela and PSR 0656+14, which
have also been detected as gamma-ray pulsars, to constrain the phase space of
obliquity and observer angles required to reproduce the observed X-ray pulsed
fractions and pulse widths. These geometrical constraints derived from the
X-ray light curves are explored for various assumptions about surface
temperature distribution and flux anisotropy caused by the magnetized
atmosphere. We include curved spacetime effects on photon trajectories and
magnetic field. The observed gamma-ray pulse profiles are double peaked with
phase separations of 0.4 - 0.5 between the peaks. Assuming that the gamma-ray
profiles are due to emission in a hollow cone centered on the magnetic pole, we
derive the constraints on the phase space of obliquity and observer angles, for
different gamma-ray beam sizes, required to produce the observed gamma-ray peak
phase separations. We compare the constraints from the X-ray emission to those
derived from the observed gamma-ray pulse profiles, and find that the
overlapping phase space requires both obliquity and observer angles to be
smaller than 20-30 degrees, implying gamma-ray beam opening angles of at most
30-35 degrees.Comment: 29 pages, 9 embedded figures, AASTEX v.4, To appear in ApJ, June 20,
1998 (Vol. 499
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