Pair creation above pulsar polar caps - Steady flow in the surface acceleration zone and polar CAP X-ray emission

1981 ◽  
Vol 248 ◽  
pp. 1099 ◽  
Author(s):  
J. Arons
Keyword(s):  
Steady Flow ◽  
Pair Creation ◽  
Polar Cap ◽  
X Ray ◽  
Polar Caps ◽  
Acceleration Zone

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 Emission of particles and photons in the pulsar polar cap

2000 ◽  
Vol 177 ◽  
pp. 473-478
Author(s):  
A. I. Tsygan
Keyword(s):  
Gamma Ray ◽  
Radio Pulsars ◽  
Polar Cap ◽  
X Ray ◽  
Polar Caps ◽  
Electron Positron ◽  
Inertial Frames ◽  
General Relativistic ◽  
Star Surface ◽  
General Relativistic Effect

AbstractWe study emission of particles and photons from a pulsar polar cap. The Goldreich-Julian model for the regime of free emission of charged particles from the neutron star surface is used. In this case the electric field is generated due to the general relativistic effect of dragging of inertial frames. The spectra and shapes of gamma-ray pulses, the parameters of the electron-positron plasma and the intensity of X-ray emission from hot spots in the polar region of radio pulsars are discussed. The effect of non-dipole magnetic field on X-ray emission of polar caps is considered. It is shown that the increase of magnetic line curvature leads to much smaller temperatures and X-ray luminosities of the polar caps as compared with the purely dipole field.

scholarly journals Observational Consequences of Polar Cap Theories

1981 ◽  
Vol 95 ◽  
pp. 99-102
Author(s):  
Andrew F. Cheng
Keyword(s):  
Magnetic Field ◽  
Temporal Modulation ◽  
Polar Cap ◽  
Ion Outflow ◽  
X Ray ◽  
Surface Magnetic Field ◽  
Polar Caps ◽  
Temperature Oscillations ◽  
Field Lines ◽  
Positive Ion

Possible observational consequences are outlined for pulsar models with positive ion outflow at the polar caps together with e+-e− pair production discharge there. A characteristic thermal x-ray luminosity is maintained by discharge heating in regions of positive current outflow. A decrease in polar cap thermal x-ray emission may occur during radio nulls. Two mechanisms are identified which can yield temporal modulation of the outflowing ion and e+-e− plasmas, and which may lead to modulation of coherent radio emission on observed microstructure timescales. These are: (1) polar cap temperature oscillations which occur preferentially in pulsars of low surface magnetic field, and (2) the tendency of sparks to migrate toward the convex side of the magnetic field lines.

scholarly journals Pulsar Death at an Advanced Age

1996 ◽  
Vol 160 ◽  
pp. 177-178
Author(s):  
Jonathan Arons
Keyword(s):  
Radio Emission ◽  
Large Scale ◽  
High Energy ◽  
Pair Creation ◽  
High Energy Particle ◽  
Polar Cap ◽  
Pulsar Radio ◽  
Polar Caps ◽  
Low Altitude ◽  
Pulsar Radio Emission

Not long ago Rankin (1990) presented strong evidence in favor of a low altitude (r≈R*) dipole geometry for the site of the core component of pulsar radio emission. Arons (1993) gave evidence that spun up millisecond pulsars must have a substantially dipolar large scale field at low altitute. Electron-positron pair creation at low altitude above the polar caps has long been hypothesized to be an essential ingredient of pulsar radio emission. If so, all observed pulsars must lie in the region ofP−Ṗspace where polar cap acceleration has sufficient vigor to lead to the copious pair production. Yet, to date, allinternally consistenttheories of polar cap pair creation have required hypothesizing a large scale (eg, quadrupole) component of the magnetic field with strength comparable to that of the dipole, in contradiction with the evidence in favor of an apparently dipolar low altitude geometry. The internally consistent theories also violate other observational constraints. The discharge models of Ruderman and Sutherland (1975), Gurevich and Istomin (1985), and Jones (1977, 1978, 1979) all accelerate equal, counterstreaming flows of electrons and positrons, thus putting one half of the particle acceleration energy into high energy particle and photon bombardment of the polar caps. The heating causes pulsed thermal X-ray emission from hot spots in excess of what is seen (Ogelman 1993). While the Arons and Scharlemann (1979) model does not have this problem, since the space charge in the starvation zone above the polar cap is made up almost entirely of the outbound beam, in star centered dipole geometry it dramatically fails to account for pulsar emission over most of theP−Ṗdiagram and predicts radio polarization variations in contradiction to the observations (Narayan and Vivekanand 1982).

scholarly journals Surface magnetic fields in pulsars

2008 ◽  
Vol 4 (S259) ◽  
pp. 131-132
Author(s):  
George I. Melikidze ◽  
Janusz Gil
Keyword(s):  
Magnetic Field ◽  
Hot Spot ◽  
Black Body ◽  
Small Scale ◽  
Radio Pulsars ◽  
Polar Cap ◽  
X Ray ◽  
Surface Magnetic Field ◽  
Bolometric Luminosity ◽  
Polar Caps

AbstractObservations of hot-spot thermal X-ray emission from radio pulsars implicate that surface magnetic field (SMF) at the polar cap is much stronger than the conventional dipolar component estimated from the pulsar spin-down. This strongly suggests that SMF is dominated by the crust anchored small scale magnetic field. We present the observed values of black body temperature and bolometric luminosity of X-ray emission from hot polar caps of a number of pulsars. In all cases the inferred value of SMF is close to 1014 G.

scholarly journals An Emission Line in the Hard X-Ray Spectrum of Hercules X-1: Quantized Cyclotron Emission from the Neutron Star

1977 ◽  
Vol 43 ◽  
pp. 34-34
Author(s):  
W. Pietsch ◽  
C. Reppin ◽  
R. Staubert ◽  
J. Truemper ◽  
W. Voges ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Field Strength ◽  
Second Harmonic ◽  
Narrow Line ◽  
Electron Cyclotron Emission ◽  
Polar Cap ◽  
Astrophysical Application ◽  
X Ray ◽  
Cyclotron Emission

A four hour balloon observation of HERC X-l during the 'On-state' in the 35 day cycle was performed on May 3rd, 1976. The 1.24 second pulsations show a pulsed fraction of 58 ± 8% in the 18-31 KeV interval. A pulsed flux (1.24 sec) was discovered in the 31-88 KeV interval with a pulsed fraction of 51 ± 14%. The spectrum of the pulsed flux can be represented up to 50 KeV by an exponential distribution with KT approximately 8 KeV. At approximately 58 KeV a strong and narrow line feature occurs which we interpret as electron cyclotron emission (ΔN = 1 Landau transition) from the polar cap plasma of the rotating neutron star. The corresponding magnetic field strength is approximately 5 x 1012 Gauss, neglecting gravitational red shift. There is evidence for a second harmonic at approximately 110 KeV (ΔN = 2 ).The astrophysical application of this discovery will be discussed in some detail.

scholarly journals Extreme Ultraviolet Spectroscopy of Magnetic Cataclysmic Variables

1996 ◽  
Vol 152 ◽  
pp. 309-316
Author(s):  
Frits Paerels ◽  
Min Young Hur ◽  
Christopher W. Mauche
Keyword(s):  
High Resolution ◽  
White Dwarf ◽  
Extreme Ultraviolet ◽  
Cataclysmic Variables ◽  
Ultraviolet Spectroscopy ◽  
Temperature Structure ◽  
Polar Cap ◽  
Ultraviolet Emission ◽  
X Ray ◽  
Magnetic Cataclysmic Variables

A longstanding problem in the interpretation of the X-ray and extreme ultraviolet emission from strongly magnetic cataclysmic variables can be addressed definitively with high resolution EUV spectroscopy. A detailed photospheric spectrum of the accretion-heated polar cap of the white dwarf is sensitive in principle to the temperature structure of the atmosphere. This may allow us to determine where and how the bulk of the accretion energy is thermalized. The EUVE data on AM Herculis and EF Eridani are presented and discussed in this context.

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 A Geometrical origin of the Pulsar Core and Conal Emissions

1996 ◽  
Vol 160 ◽  
pp. 229-230 ◽  
Author(s):  
R.C. Kapoor ◽  
C.S. Shukre
Keyword(s):  
Polar Angle ◽  
Quadratic Equation ◽  
Magnetic Axis ◽  
Polar Cap ◽  
The Core ◽  
The North ◽  
Polar Caps ◽  
Inclination Angles ◽  
Field Geometry ◽  
Field Lines

We have analysed the dipole magnetic field geometry for the general case of an oblique rotator and have found that open field lines which define the polar cap divide into two branches (Kapoor and Shukre 1996) which appear naturally relevant for distinguishing the core and conal emissions. The polar cap shape is actually determined by a quadratic equation having two roots leading to two values of the polar angle,θ+andθ−with respect to the magnetic axis for a given azimuth φ. For the north pole bothθ+andθ−branches are shown as polar plots in Fig. 1 for various inclination angles α and a typical pulsar period. The discussion of pulsar polar caps hitherto (e.g. Biggs 1990) had not distinguished between theθ+and theθ−solutions. The region defined by theθ+solution is completely contained inside the polar cap. It has a peculiar triangular shape whose lowest vertex is always on the magnetic axis. This naturally suggests an identification of theθ+and theθ−regions with the core and conal emission zones.

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