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.

scholarly journals DETECTION OF MAGNETIC INCLINATION ANGLE BY SEA TURTLES: A POSSIBLE MECHANISM FOR DETERMINING LATITUDE

1994 ◽  
Vol 194 (1) ◽  
pp. 23-32 ◽  
Author(s):  
K Lohmann ◽  
C Lohmann
Keyword(s):  
Inclination Angle ◽  
Sea Turtles ◽  
Positional Information ◽  
Compass Orientation ◽  
Loggerhead Sea Turtles ◽  
Southern Boundary ◽  
The North ◽  
Magnetic Inclination ◽  
Inclination Angles ◽  
Field Lines

For animals that migrate long distances, the magnetic field of the earth provides not only a possible cue for compass orientation, but a potential source of world-wide positional information. At each location on the globe, the geomagnetic field lines intersect the earth's surface at a specific angle of inclination. Because inclination angles vary with latitude, an animal able to distinguish between different field inclinations might, in principle, determine its approximate latitude. Such an ability, however, has never been demonstrated in any animal. We studied the magnetic orientation behavior of hatchling loggerhead sea turtles (Caretta caretta L.) exposed to earth-strength magnetic fields of different inclinations. Hatchlings exposed to the natural field of their natal beach swam eastward, as they normally do during their offshore migration. In contrast, those subjected to an inclination angle found on the northern boundary of the North Atlantic gyre (their presumed migratory path) swam south-southwest. Hatchlings exposed to an inclination angle found near the southern boundary of the gyre swam in a northeasterly direction, and those exposed to inclination angles they do not normally encounter, or to a field inclination found well within the northern and southern extremes of the gyre, were not significantly oriented. These results demonstrate that sea turtles can distinguish between different magnetic inclination angles and perhaps derive from them an approximation of latitude. Most sea turtles nest on coastlines that are aligned approximately north­south, so that each region of nesting beach has a unique inclination angle associated with it. We therefore hypothesize that the ability to recognize specific inclination angles may largely explain how adult sea turtles can identify their natal beaches after years at sea.

scholarly journals Storm enhanced density: magnetic conjugacy effects

2007 ◽  
Vol 25 (8) ◽  
pp. 1791-1799 ◽  
Author(s):  
J. C. Foster ◽  
W. Rideout
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Ionospheric Disturbance ◽  
Polar Regions ◽  
The North ◽  
Polar Caps ◽  
Source Regions ◽  
Field Lines ◽  
Magnetic Conjugacy ◽  
Early Phases

Abstract. In the early phases of a geomagnetic storm, the low and mid-latitude ionosphere are greatly perturbed. Large SAPS electric fields map earthward from the perturbed ring current overlapping and eroding the outer plasmasphere and mid-latitude ionosphere, drawing out extended plumes of storm enhanced density (SED). We use combined satellite and ground-based observations to investigate the degree of magnetic conjugacy associated with specific features of the stormtime ionospheric perturbation. We find that many ionospheric disturbance features exhibit degrees of magnetic conjugacy and simultaneity which implicate the workings of electric fields. TEC enhancements on inner-magnetospheric field lines at the base of the SED plumes exhibit localized and longitude-dependent features which are not strictly magnetic conjugate. The SED plumes streaming away from these source regions closely follow magnetic conjugate paths. SED plumes can be used as a tracer of the location and strength of disturbance electric fields. The SED streams of cold plasma from lower latitudes enter the polar caps near noon, forming conjugate tongues of ionization over the polar regions. SED plumes exhibit close magnetic conjugacy, confirming that SED is a convection electric field dominated effect. Several conclusions are reached: 1) The SED plume occurs in magnetically-conjugate regions in both hemispheres. 2) The position of the sharp poleward edge of the SED plume is closely conjugate. 3) The SAPS electric field is observed in magnetically conjugate regions (SAPS channel). 4) The strong TEC enhancement at the base of the SED plume in the north American sector is more extensive than in its magnetic conjugate region. 5) The entry of the SED plume into the polar cap near noon, forming the polar tongue of ionization (TOI), is seen in both hemispheres in magnetically-conjugate regions.

scholarly journals A model for PSR J0437-4715

1996 ◽  
Vol 160 ◽  
pp. 213-214
Author(s):  
Janusz Gil ◽  
Agnieszka Krawczyk
Keyword(s):  
Magnetic Axis ◽  
Central Core ◽  
Polar Cap ◽  
Pulsar Emission ◽  
The Core ◽  
First Case ◽  
Central Column ◽  
The Mean ◽  
Multiple Component ◽  
Real Challenge

We present the modelling results of full polarization data of the PSR J0437-4715, recently published by Manchester & Johnston (1995). This pulsar presents a real challenge for pulsar modelling because of seven clear components in its mean profile. In terms of the conal model of pulsar emission this is the first case indicating three distinct cones surrounding the central core beam. We have attempted to model this pulsar and obtained a very satisfactory fit to the data. We succeded to reproduce the complexities of the multiple component profile and polarization properties.To model the radiation from PSR J0437-4715 we use the method presented in Gil et al. (1995 and references therein). We assume that subpulses in single pulses correspond to the subpulse-associated plasma columns distributed within the overall pulsar beam. Each column represents a gaussian intensity distribution. These columns rotate more or less regularly around the magnetic axis. The exception is the central column directed almost along the magnetic axis defined by the local surface magnetic pole. This column corresponds to the core beam and consequently to the core component in our model. Outer columns rotating at some distances from the core axis will form a number of coaxial conal beams corresponding to the conal profile components. Figure 1a represents a projection of the subpulse-associated columns onto the polar cap while Fig. lb represents schematically a corresponding multiconal structure of the average beam. The initial positions, the characteristic dimensions and the relative amplitudes of the subpulse spots (Fig. 1a) have been estimated from the mean profile (Fig. 2b). We assume that the subpulse spots are separated from each other by distances comparable with their sizes (Fig. 1a). The very large polar cap with the radiusrp= 1.4 · 104P−1/2cm ≈ 1900 m as compared with the characteristic subpulse spot dimensionD≈ 300 m allows three conal rings surrounding the central core beam (Fig. 1b).

scholarly journals An Empirical Theory of Pulsar Emission

1992 ◽  
Vol 128 ◽  
pp. 132-139
Author(s):  
Joanna M. Rankin
Keyword(s):  
Emission Characteristics ◽  
Pencil Beam ◽  
Empirical Theory ◽  
Polar Cap ◽  
Pulsar Emission ◽  
The Core ◽  
Pulsar Radiation ◽  
Starting Point ◽  
Major Species ◽  
Field Lines

AbstractA system of pulsar profile classification is used as a starting point to study the emission characteristics of pulsars. Two types or mechanisms of pulsar radiation are identified which combine geometrically to produce five major species of profile. The core emission, which forms a pencil beam of radiation, is apparently produced close to the stellar surface throughout the entire polar cap region by low γ particles. The conal emission, which consists of a hollow conical beam, then seems to be emitted at heights of 10 to 20 stellar radii by currents of high γ particles travelling along some of the most peripheral of the “open” field lines.

scholarly journals High-energy accelerators above pulsar polar caps

2000 ◽  
Vol 177 ◽  
pp. 479-480
Author(s):  
R. X. Xu ◽  
G. J. Qiao ◽  
B. Zhang
Keyword(s):  
Neutron Stars ◽  
Lorentz Factor ◽  
High Energy ◽  
Magnetic Axis ◽  
Rotational Axis ◽  
Polar Cap ◽  
Strange Stars ◽  
Polar Caps ◽  
Axis Parallel

AbstractSimilar to the terrestrial collision accelerators of e±, another kind of accelerator is above a positively or negatively charged pulsar polar cap. In the case of pulsars with magnetic axis parallel (anti-parallel) to rotational axis, relativistic e+(e−) with Lorentz factorγ~ 106hit the electrons in the polar caps. These scenarios are investigated both for pulsars being BSSs (bare strange stars) and for pulsars being NSs (neutron stars). Such a study may be valuable to differentiate NSs and BSSs observationally.

scholarly journals The magnetic field structure in the multi-source magnetized core NGC 2024 FIR 5

2008 ◽  
Vol 4 (S259) ◽  
pp. 53-60
Author(s):  
Felipe de O. Alves ◽  
J. M. Girart ◽  
S.-P. Lai ◽  
R. Rao ◽  
Q. Zhang
Keyword(s):  
Magnetic Field ◽  
Dust Emission ◽  
Field Structure ◽  
Magnetic Field Structure ◽  
The Core ◽  
Evolutionary Scenario ◽  
Field Geometry ◽  
Field Lines ◽  
Grain Properties ◽  
The Magnetic Field

AbstractThis work reports high resolution SMA polarimetric observations toward NGC 2024 FIR 5, a magnetized core previously found to harbour protostars. Our 345 GHz data indicates the presence of an extended dust emission associated with the dense core where the protostars are embedded. The 3σ polarized intensity shows depolarization toward the peak of Stokes I emission. This diminishing polarized flux implies that the alignment efficiency of the core dust grains is low within higher column densities where grain properties are likely different. The derived magnetic field geometry exhibits pinched field lines which are typical in evolved supercritical clouds where the magnetic field no longer support the core from collapsing. As a consequence for protostars, the gravitational pulling along the disk's long axis makes an equatorial bend to the field lines that, in turn, results in a hourglass shape. The SMA field structure agrees perfectly with the BIMA map. However, models are still necessary to provide a complete description of the evolutionary scenario of FIR 5.

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 Evolution and Radiation in Pulsar Polar Cap Models

1981 ◽  
Vol 95 ◽  
pp. 87-98 ◽  
Author(s):  
M. Ruderman
Keyword(s):  
Mode Switching ◽  
Orthogonal Polarization ◽  
Polar Cap ◽  
Mature Adult ◽  
Inverse Compton Scattering ◽  
Polar Caps ◽  
Double Beam ◽  
Linearly Polarized ◽  
Field Lines ◽  
Fe Ions

Positively charged particle emission from pulsar polar caps evolves through many stages as the cap temperature cools. In “infant” pulsars, stripped Fe ions interact with secondary e± from a 1012 V discharge maintained just above the cap to give coherent radio emission at very high frequencies in a very broad beam. In “adolescent” pulsars such as the Crab and Vela, lower energy Fe ions interact with streams of protons produced in the surface by photonuclear reactions to give lower frequency highly linearly polarized radiation. There is no cap e± discharge. In mature “adult” pulsars proton and/or Fe ion streams from discharge heated patches on the polar cap interact with a relativistic e± plasma to give coherent radio subpulse beams which can drift, have strong submillisecond modulations, and orthogonal polarization mode switching. Young pulsars, and some older ones, can support additional more energetic e± discharges on some open field lines in the outer magnetosphere. These all give strong double beams of GeV γ-rays and weaker γ-ray beams above ~ 1012 eV. With Crab pulsar parameters an e± plasma associated with such a discharge also can give optical and X-ray double beams. If illuminated by the normal pulsar beam (precursor) coherent inverse Compton scattering also contributes a double beam of harder radio frequencies.

scholarly journals Meso-scale aurora within the expansion phase bulge

2006 ◽  
Vol 24 (8) ◽  
pp. 2209-2218 ◽  
Author(s):  
N. Partamies ◽  
K. Kauristie ◽  
E. Donovan ◽  
E. Spanswick ◽  
K. Liou
Keyword(s):  
High Energy ◽  
Closed Field ◽  
Polar Cap ◽  
Expansion Phase ◽  
The North ◽  
Bursty Bulk Flow ◽  
Central Plasma ◽  
Field Lines ◽  
Auroral Arcs ◽  
Meso Scale

Abstract. We present ground-based optical, riometer and magnetometer recordings together with Polar UVI and GOES magnetic field observations of a substorm that occurred over Canada on 24 November 1997. This event involved a clear optical onset followed by poleward motion of the aurora as a signature of an expanding auroral bulge. During the expansion phase, there were three distinct types of meso-scale (10–1000 km) auroral structures embedded in the bulge: at first a series of equatorward moving auroral arcs, followed by a well-defined spiral pair, and finally north-south directed aurora (a streamer). The spirals occurred several minutes after the onset, and indicate a shear in the field-aligned current. The north-south aligned aurora that formed about 10 min after the onset suggest bursty bulk flow type flows taking place in the central plasma sheet. Polar UVI observations of the polar cap location indicate that the southward drifting arcs were associated with magnetospheric activity within closed field lines, while the auroral streamer was launched by the bulge reaching the polar cap boundary, i.e. the mid-tail reconnection starting on the open field lines. The riometer data imply high energy electron precipitation in the vicinity of the the poleward moving edge of the auroral bulge, starting at the onset and continuing until the formation of the north-south structure. In this paper, we examine this evolving auroral morphology within the context of substorm theories.

scholarly journals North Atlantic warming over six decades drives decreases in krill abundance with no associated range shift

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Martin Edwards ◽  
Pierre Hélaouët ◽  
Eric Goberville ◽  
Alistair Lindley ◽  
Geraint A. Tarling ◽  
...  
Keyword(s):  
North Atlantic ◽  
Range Shift ◽  
The Core ◽  
Krill Abundance ◽  
The North ◽  
Living Space ◽  
Warming Climate ◽  
Two Temperatures ◽  
The North Atlantic

AbstractIn the North Atlantic, euphausiids (krill) form a major link between primary production and predators including commercially exploited fish. This basin is warming very rapidly, with species expected to shift northwards following their thermal tolerances. Here we show, however, that there has been a 50% decline in surface krill abundance over the last 60 years that occurred in situ, with no associated range shift. While we relate these changes to the warming climate, our study is the first to document an in situ squeeze on living space within this system. The warmer isotherms are shifting measurably northwards but cooler isotherms have remained relatively static, stalled by the subpolar fronts in the NW Atlantic. Consequently the two temperatures defining the core of krill distribution (7–13 °C) were 8° of latitude apart 60 years ago but are presently only 4° apart. Over the 60 year period the core latitudinal distribution of euphausiids has remained relatively stable so a ‘habitat squeeze’, with loss of 4° of latitude in living space, could explain the decline in krill. This highlights that, as the temperature warms, not all species can track isotherms and shift northward at the same rate with both losers and winners emerging under the ‘Atlantification’ of the sub-Arctic.

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