Condensed Surfaces of Magnetic Neutron Stars and Particle Acceleration Above Pulsar Polar Caps

2008 ◽  
Author(s):  
Zach Medin ◽  
Dong Lai ◽  
C. Bassa ◽  
Z. Wang ◽  
A. Cumming ◽  
...  
Keyword(s):  
Particle Acceleration ◽  
Neutron Stars ◽  
Polar Caps

scholarly journals Future Facilities for Gamma-Ray Pulsar Studies

2004 ◽  
Vol 218 ◽  
pp. 399-406
Author(s):  
D. J. Thompson
Keyword(s):  
Particle Acceleration ◽  
Neutron Stars ◽  
Gamma Ray ◽  
Large Area ◽  
Space Telescope ◽  
High Energies ◽  
Interaction Processes ◽  
Very High ◽  
Insight Into

Pulsars seen at gamma-ray energies offer insight into particle acceleration to very high energies, along with information about the geometry and interaction processes in the magnetospheres of these rotating neutron stars. During the next decade, a number of new gamma-ray facilities will become available for pulsar studies. This brief review describes the motivation for gamma-ray pulsar studies, the opportunities for such studies, and some specific discussion of the capabilities of the Gamma-ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT) for pulsar measurements.

scholarly journals Radiation Gas Dynamics of Polar Cap Accretion onto Magnetized Neutron Stars

1987 ◽  
Vol 125 ◽  
pp. 246-246
Author(s):  
Richard I. Klein ◽  
Jonathan Arons
Keyword(s):  
Neutron Stars ◽  
Radiation Pressure ◽  
Operator Splitting ◽  
High Energy ◽  
Plasma Pressure ◽  
Analytical Models ◽  
High Luminosity ◽  
Polar Cap ◽  
Operator Splitting Methods ◽  
Polar Caps

We present results of the first self-consistent, time-dependent, 2-D calculations of the accretion of plasma onto polar caps of high luminosity (L*>1036erg-s−1) magnetized neutron stars. We follow the temporal and spatial evolution of three fluids, electrons, ions and photons in a superstrong (B=3×1012 Gauss) dipole magnetic field where radiation pressure dominates plasma pressure by solving coupled 2-D equations of radiation hydrodynamics. We have included several physical processes in the radiation-plasma coupling in superstrong magnetic fields (Klein, et al., 1984, Santa Cruz Workshop on High Energy Transients, and Arons, this conference). We solve the resulting system of coupled 2-D PDEs on a Cray XMP-48 by applying implicit finite-difference techniques with iterative operator splitting methods. We present results for two models of 5×1037 erg-s and 1.5×1038 erg-s−1 super-Eddington luminosity on one polar cap, each having initial mass flux independent of co-latitude of a field lines footprint. We find (a) Radiation develops a broad transverse fan beam that emerges from an annulus 0.2–0.5km above the polar cap. (b) The beam profile is determined by advective trapping of radiation in optically thick (τ11,τ⊥ ≈103) flow. Here the time for diffusion of radiation up through the accretion column is ≫ the time for downward advection. (c) There is a three fluid nonequilibrium with Ti≫Tγ≥Te. (d) Maximum photon temperature of ≈ 10–20 keV in the fan beam is in the observed range. (e) Cyclotron emission ≫ bremsstrahlung as a source of photons. (f) At early times (≪lms) radiation pressure strongly decelerates flow to 10−3 of freefall in central regions of accretion column resulting in a density mound, but plasma freefalls down the sides of the column. (g) Analytical models have reasonable agreement with numerical calculations; velocity and energy density roughly Gaussian transversally and exponential vertically, until the onset of “photon bubbles” after several dynamical times (∼lms). (h) Multiple “photon bubbles” rising subsonically in the accretion column form in the high luminosity model. We believe the photon bubbles to be a possible consequence of overstable convection in super-Eddington flows. These photon bubbles could be observable as 10–100μs fluctuations in the emergent flux and, thus, be an important diagnostic for inhomogeneous structure of the column.

scholarly journals Acceleration Processes for Gamma-Ray Bursts

1994 ◽  
Vol 142 ◽  
pp. 869-876 ◽  
Author(s):  
Igor G. Mitrofanov
Keyword(s):  
Particle Acceleration ◽  
Electric Field ◽  
Neutron Stars ◽  
Gamma Rays ◽  
Gamma Ray ◽  
Initial Energy ◽  
Gamma Ray Bursts ◽  
Acceleration Of Particles ◽  
Radiation Mechanisms ◽  
Radiative Pressure

AbstractIs it shown that for those astronomical models of cosmic gamma-ray bursts (GRBs) which are associated with galactic neutron stars (NSs), the initial energy of the outburst could be converted to gamma-rays through processes of particle acceleration. The main emission mechanisms are considered for two basic alternatives, when particles are accelerated either by radiative pressure or by an electric field.Subject headings: acceleration of particles — gamma rays: bursts — radiation mechanisms: nonthermal

scholarly journals Accretion onto Magnetized Neutron Stars: Polar Cap Flow and Centrifugally Driven Winds

1987 ◽  
Vol 125 ◽  
pp. 207-225
Author(s):  
Jonathan Arons
Keyword(s):  
Angular Momentum ◽  
Neutron Star ◽  
Neutron Stars ◽  
Orbital Evolution ◽  
Time Dependent ◽  
Polar Cap ◽  
Periodic Oscillations ◽  
X Ray ◽  
Polar Caps ◽  
Basic Concepts

Some basic concepts of accretion onto the polar caps of magnetized neutron stars are reviewed. Preliminary results of new, multidimensional, time–dependent calculations of polar cap flow are outlined, and are used to suggest the possible observability of fluctuations in the X–ray intensity of accretion powered pulsars on time scales of 10–100 msec. The possible relevance of such fluctuations to Quasi–Periodic oscillations is suggested. Basic concepts of the interaction between a disk and the magnetosphere of a neutron star are also discussed. Some recent work on the disk–magnetosphere interaction is outlined, leading to the suggestion that a neutron star can lose angular momentum by driving some or all of the mass in the disk off as a centrifugally driven wind. The relevance of such mass loss to the orbital evolution of the binary is pointed out.

scholarly journals Hybrid numerical simulations of pulsar magnetospheres

2019 ◽  
Vol 491 (4) ◽  
pp. 5579-5585 ◽  
Author(s):  
Ioannis Contopoulos ◽  
Jerome Pétri ◽  
Petros Stefanou
Keyword(s):  
Particle Acceleration ◽  
Current Sheet ◽  
Electric Current ◽  
Hybrid Approach ◽  
High Energy ◽  
Basic Premise ◽  
Analytic Approximations ◽  
Polar Caps ◽  
Electron Positron ◽  
Field Lines

ABSTRACT We continue our investigation of particle acceleration in the pulsar equatorial current sheet (ECS). Our basic premise has been that the charge carriers in the current sheet originate in the polar caps as electron–positron pairs, and are carried along field lines that enter the ECS beyond the magnetospheric Y-point. In this work, we investigate further the charge replenishment of the ECS. We discovered that the flow of pairs from the rims of the polar caps cannot supply both the electric charge and the electric current of the ECS. The ECS must contain an extra amount of positronic (or electronic depending on orientation) electric current that originates in the stellar surface and flows outwards along the separatrices. We develop an iterative hybrid approach that self-consistently combines ideal force-free electrodynamics in the bulk of the magnetosphere with particle acceleration along the ECS. We derive analytic approximations for the orbits of the particles, and obtain the structure of the pulsar magnetosphere for various values of the pair formation multiplicity parameter κ. For realistic values κ ≫ 1, the magnetosphere is practically indistinguishable from the ideal force-free one, and therefore, the calculation of the spectrum of high energy radiation must rely on analytic approximations for the distribution of the accelerating electric field in the ECS.

scholarly journals Gamma-Ray Burst Theory: Back to the Drawing Board

1994 ◽  
Vol 142 ◽  
pp. 863-868
Author(s):  
Alice K. Harding
Keyword(s):  
Particle Acceleration ◽  
Neutron Stars ◽  
Gamma Rays ◽  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Acceleration Of Particles ◽  
Gamma Ray Burst ◽  
History Of ◽  
Drawing Board ◽  
The Impact

AbstractGamma-ray bursts have always been intriguing sources to study in terms of particle acceleration, but not since their discovery two decades ago has the theory of these objects been in such turmoil. Prior to the launch of Compton Gamma-Ray Observatory and observations by BATSE, there was strong evidence pointing to magnetized Galactic neutron stars as the sources of gamma-ray bursts. However, since BATSE the observational picture has changed dramatically, requiring much more distant and possibly cosmological sources. I review the history of gamma-ray burst theory from the era of growing consensus for nearby neutron stars to the recent explosion of halo and cosmological models and the impact of the present confusion on the particle acceleration problem.Subject headings: acceleration of particles — gamma rays: bursts

Particle Acceleration Zones above Pulsar Polar Caps: Electron and Positron Pair Formation Fronts

1998 ◽  
Vol 508 (1) ◽  
pp. 328-346 ◽  
Author(s):  
Alice K. Harding ◽  
Alexander G. Muslimov
Keyword(s):  
Particle Acceleration ◽  
Pair Formation ◽  
Polar Caps

scholarly journals Particle Acceleration in Spherical Wave Fields

1992 ◽  
Vol 128 ◽  
pp. 109-111
Author(s):  
K. O. Thielheim
Keyword(s):  
Particle Acceleration ◽  
Dipole Moment ◽  
Angular Velocity ◽  
Neutron Stars ◽  
Magnetic Dipole ◽  
Magnetic Dipole Moment ◽  
Spherical Wave ◽  
Particle Accelerator ◽  
Dynamic Features ◽  
Wave Fields

A magnet rotating in vacuo with its vector of angular velocity ω perpendicular to its vector of magnetic dipole moment μ is able to act as a particle accelerator. The dynamic features involved may be relevant for the understanding of rotating magnetized neutron stars as cosmic accelerators (Thielheim 1989) and may be useful for the designing of new mechanisms for accelerating devices.

Transient particle acceleration in strongly magnetized neutron stars

1991 ◽  
Vol 376 ◽  
pp. 673 ◽  
Author(s):  
Fulvio Melia ◽  
Marco Fatuzzo
Keyword(s):  
Particle Acceleration ◽  
Neutron Stars
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