Current flow and pair creation at low altitude in rotation-powered pulsars’ force-free magnetospheres: space charge limited flow

By A. N. Timokhin, J. Arons. 2012

185 citations recorded by the source corpus.

We report the results of an investigation of particle acceleration and electron-positron plasma generation at low altitude in the polar magnetic flux tubes of rotation-powered pulsars, when the stellar surface is free to emit whatever charges and currents are demanded by the force-free magnetosphere. We apply a new 1D hybrid plasma simulation code to the dynamical problem, using Particle-in-Cell methods for the dynamics of the charged particles, including a determination of the collective electrostatic fluctuations in the plasma, combined with a Monte Carlo treatment of the high-energy gamma-rays that mediate the formation of the electron-positron pairs.We assume the electric current flowing through the pair creation zone is fixed by the much higher inductance magnetosphere, and adopt the results of force-free magnetosphere models to provide the currents which must be carried by the accelerator. The models are spatially one dimensional, and designed to explore the physics, although of practical relevance to young, high-voltage pulsars. We observe novel behaviour (a) When the current density j is less than the Goldreich-Julian value (0 1), the system develops high voltage drops (TV or greater), causing emission of curvature gamma-rays and intense bursts of pair creation. The bursts exhibit limit cycle behaviour, with characteristic time-scales somewhat longer than the relativistic fly-by time over distances comparable to the polar cap diameter (microseconds). (c) In return current regions, where j/j(sub GJ) < 0, the system develops similar bursts of pair creation. These discharges are similar to those encountered in previous calculations by Timokhin of pair creation when the surface has a high work function and cannot freely emit charge. In cases (b) and (c), the intermittently generated pairs allow the system to simultaneously carry the magnetospherically prescribed currents and adjust the charge density and average electric field to force-free conditions. We also elucidate the conditions for pair creating beam flow to be steady (stationary with small fluctuations in the rotating frame), finding that such steady flows can occupy only a small fraction of the current density parameter space exhibited by the force-free magnetospheric model. The generic polar flow dynamics and pair creation are strongly time dependent. The model has an essential difference from almost all previous quantitative studies, in that we sought the accelerating voltage (with pair creation, when the voltage drops are sufficiently large; without, when they are small) as a function of the applied current.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/0238f735fd5d024bbb0b84f82879e2fe28ae36b9

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. A. Philippov
2. B. Cerutti
3. A. Spitkovsky
4. K. Parfrey
5. L. Sironi
6. J. Arons
7. D. Giannios
8. A. N. Timokhin

In Nuclear and High Energy Physics

1. A. Philippov
2. A. Spitkovsky
3. B. Cerutti
4. K. Parfrey
5. L. Sironi
6. J. Arons
7. D. Giannios
8. M. Petropoulou

Citations in the corpus

• Modelling high-energy pulsar light curves from first principles (2015, background): “However, it ignores the details of the pair creation physics which is the main focus of other studies (Timokhin & Arons 2013; Chen & Beloborodov 2014; Philippov et al. 2015).”
• Ab-initio Pulsar Magnetosphere: Particle Acceleration in Oblique Rotators and High-energy Emission Modeling (2017, background): “However, as in the case of the aligned rotator, some field lines still carry sub-GJ current, which is supported by the charge-separated outflow of electrons (Timokhin & Arons 2013; Philippov et al. 2015a; Gralla et al. 2016).”
• Particle acceleration in axisymmetric pulsar current sheets (2014, background): “In principle, one should model the full electromagnetic cascade to obtain a self-consistent injection of pairs into the magnetosphere (e.g., Timokhin & Arons 2013; Chen & Beloborodov 2014).”