Langmuir Solitons and Pulsar Radio Emission

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Langmuir Solitons and Pulsar Radio Emission U. A. Mofiz Department of Mathematics and Natural Sciences, BRAC University, 66 Mohakhali, Dhaka-1212, Bangladesh Email: mofiz@bracu.ac.bd Abstract Nonlinear propagation of electrostatic wave modes in ultrarelativistic dense elelectron-positron gravito-plasma at the polar cap region of pulsar magnetosphere is considered. A nonlinear Schrödinger equation is obtained from the reductive perturbation method which predicts the existence of Langmuir dark solitons. Amplitudes and widths of dark solitons are investigated for different temperatures of the plasma. Relevance of the existence stable dark solitons to the pulsar radio emission is discussed. Key words: Pulsar magnetosphere, electron-positron plasma, Langmuir dark solitons ,pulsar radio emission. Introduction Pulsars are celestial sources that believe to be rotating neutron stars producing light-house like beams of radio emissions from the magnetic poles. As shown by Goldreich and Julian (1969)[1] the rotating magnetic dipole produces a quadrupole electric field whose component parallel to the open magnetic field lines at the poles extracts particles very effectively from neutron star surface and accelerates them to highly relativistic energies. Thus, the magnetosphere is filled with plasma which shields the electric field. Complete shielding is established when the net charge reaches nGJ - the Goldreich -Julian charge density. The Lorentz factors of the accelerated particles reach about 106 and they emit hard curvature radiations that propagate at a sufficient angle to the magnetic field so that significant pair production of electron-positron can occur (Erber 1966)[2]. It is commonly accepted that the newly created particles produce more pairs by emitting energetic synchrotron or curvature radiation. As a result an avalanche of

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