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Paper: Partially Screened Polar Gap in Pulsars
Volume: 404, The Eighth Pacific Rim Conference on Stellar Astrophysics: A Tribute to Kam Ching Leung
Page: 131
Authors: Melikidze, G.; Gile, J.
Abstract: We demonstrate that the features of the partially screened polar gap define properties of both X and radio emission of pulsars. The model implies that the temperature of the polar cap surface is almost equal to the co called critical temperature which is defined by the strength of the magnetic field at the stellar surface. Parameters of observed thermal X-ray emission derived from the blackbody fit usually imply the surface of the hot spot to be much smaller than the conventional polar cap area, which can be naturally explained by assuming that the geometry and strength of the magnetic field at the stellar surface differ essentially from the pure star centered dipole field. The model assumes that the source of the pulsar activity is associated with the Partially Screened Gap (PSG) operating in the inner acceleration region above the polar cap where the electric field has a component along the magnetic field lines. Particles (electrons and positrons) are accelerated in both directions: outward and toward the stellar surface. Consequently, outstreaming particles generate the magnetospheric Xray emission while the backstreaming particles heat the surface and provide necessary energy for the thermal emission. The model assumes that the potential drop near the stellar surface is partially screened by the positive ions. Therefore the accelerating potential drop depends on the temperature of the polar cap. If temperature increases the density of the charge also increases, which causes reduction of the potential drop and consequently reduction of heating rate. As a result the surface temperature should be stabilized near the critical value. The model described above predicts certain dependence between the hot spot area and temperature, derived from the black body fitting to the spectra of the neutron star thermal X-ray emission. The temperature should always equal to the critical temperature. On the other hand the critical temperature is defined by the strength of the magnetic field and the cohesive energy of the crust material. As a result the black body spectra fitting parameters (temperature and hot spot area) should not be treated as independent parameters.
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