EDP Sciences
Free access
Volume 416, Number 3, March IV 2004
Page(s) 1139 - 1147
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20034343

A&A 416, 1139-1147 (2004)
DOI: 10.1051/0004-6361:20034343

Electrostatic instability in electron-positron pairs injected in an external electric field

K. Asano and F. Takahara

Department of Earth and Space Science, Osaka University, Toyonaka 560-0043, Japan
    e-mail: takahara@vega.ess.sci.osaka-u.ac.jp
(Received 17 September 2003 / Accepted 28 November 2003 )

Motivated by the particle acceleration problem in pulsars, we numerically investigate electrostatic instability of electron-positron pairs injected in an external electric field. The electric field is expected to be so strong that we cannot neglect effects of spatial variation in the 0th order distribution functions on the scale of the plasma oscillation. We assume that pairs are injected mono-energetically with 4-velocity u0>0 in a constant external electric field by which electrons (positrons) are accelerated (decelerated). By solving linear perturbations of the field and distribution functions of pairs, we find a new type of electrostatic instability. The properties of the instability are characterized by u0 and the ratio R of the braking time-scale (determined by the external electric field) to the time-scale of the plasma oscillation. The growth rate is as large as a few times the plasma frequency. We discuss the possibility that the excited waves prevent positrons from returning to the stellar surface.

Key words: instabilities -- plasmas -- stars: pulsars: general

Offprint request: K. Asano, asano@vega.ess.sci.osaka-u.ac.jp

© ESO 2004